It's not just pricey imported chocolate bars taking up shelf space and boasting how dark they are. Take a look at the dark chocolate M&M's and dark Hershey's Kisses.

There's method to this darkness. It just so happens that researchers recently have focused on the potential health benefits of dark chocolate, which ultimately could translate into big profits. In fact, candy makers are reporting an increased demand for the biting taste of dark chocolate.

So far, candy packaging doesn't claim such benefits, but some labels now billboard the candy's ''percent cocoa'' content - 50, 60, 70 percent. That's because the higher the cocoa content, nutrition researchers say, the better.

Chocolate is made from cacao beans, a great source of flavonoids, a beneficial plant compound that's in other good stuff including green and red fruits and vegetables, red wine and green tea.

''The dark color serves as a marker that it's got more of the flavonoids,'' said Pete Beyer, associate dietetics and nutrition professor at the University of Kansas.

What good are flavonoids? Scientists are finding that higher blood levels of flavonoids create good cardiovascular effects, the kind that may lower the risk of heart disease and certain cancers.

For dark chocolate lovers, the research, much of it sponsored by candy maker Mars Inc., is promising.

A report in the March issue of the American Journal of Clinical Nutrition linked high-flavonoid dark chocolate with improved blood pressure.

One study showed that dark chocolate consumption reduced the ''stickiness'' of blood, reducing clots and clumps, an aspirinlike effect.

Another showed that dark chocolate improved blood vessel function, which could benefit cardiovascular health.

Another study found that a diet that included dark chocolate increased good cholesterol and helped prevent bad cholesterol from oxidizing.

These effects aren't unique to the plant compounds in dark chocolate. Diana Rodenberg, registered dietician at St. Luke's Hospital in Kansas City, Mo., said that these are the same antioxidant effects people get from fruits and vegetables.

Carl Keen, chocolate researcher and nutrition professor at the University of California-Davis, said that an initial research question about dark chocolate was whether the body actually absorbs its beneficial compounds. The answer was yes.

''You can consume a cocoa beverage or chocolate bar rich in flavonoids, and within 30 minutes to an hour you can see them in the bloodstream,'' Keen said.

Researchers followed up by showing some positive effects of those plant-based compounds.

Still, confirming the effects is a step removed from saying that flavonoids in dark chocolate actually improve heart health.

''It doesn't prove anything, but it's looking awfully good,'' Keen said.

Experts point out at least two other big caveats: One is the calorie problem. The other has to do with processing, which can greatly reduce the flavonoids in chocolate, including the dark kind.

In some studies that showed benefits, participants were given 100 grams of dark chocolate. That's 3.5 ounces and 500 calories, way more than most people should add to their diets. A more reasonable amount, say a bit less than half that, is about 200 calories.

By contrast, a half-cup serving of nutrient-rich broccoli has just 14 calories. Green tea, another great source of flavonoids, has no calories.

''There may be some health benefits to dark chocolate, but you don't want to go overboard,'' Rodenberg said.

Dark chocolate belongs in the category of protective food, Beyer said, but it doesn't get a spot on the dinner plate. If you set aside 200 to 300 calories for a treat during the day, it's much better to eat some dark chocolate than to down a bag of potato chips or a can of soda, he said.

''It's not a bad choice to spend your discretionary calories on dark chocolate,'' Beyer said.

Bonnie Liebman, nutrition director at the Center for Science in the Public Interest, isn't ready to call dark chocolate nutritious. The gap between recent research and improved heart health is wide, she said. And she's worried the ''good for you'' message will overshadow the very real calorie concerns.

''We all hope that flavonoids and antioxidants turn out to reduce heart disease and cancer, but we don't have that evidence yet,'' she said. ''We've been wrong about other antioxidants, with the most recent example in vitamin E.''

Small amounts of chocolate candy pack a lot of calories, she said.

''My concern is that until recently, people ate chocolate sparingly because they knew it wasn't broccoli. They knew they had to be cautious,'' said Liebman, who noted that she isn't opposed to small amounts of candy as a treat. ''There may be some people who can afford the calories, but they're in the minority.''

The other caveat: processing. Unfortunately, just because the package says ''dark'' doesn't mean the chocolate inside is packed with flavonoids. There's no way for the consumer to know, Keen said, and we are years away from getting compounds such as flavonoids listed on labels.

Some flavonoids are lost in the fermenting of cacao beans and also when alkali is used in the chocolate-making process. The labels of some chocolate products note the use of alkali.

From candy bars to semisweet morsels for baking, Keen said, it's a question mark how much of the flavonoids have survived the processing.

Generally, dark chocolate products should have more flavonoid content than milk chocolate products, but individually there's no way to know, he said.

One hint comes from companies that list ''cocoa content'' percentages. Packaging for Ghirardelli chocolate squares boldly states ''60 percent cocoa'' and Lindt dark chocolate bars proclaim ''70 percent cocoa.''

In the past, food manufacturers worked to remove flavonoids or otherwise try to blunt their bitter taste. Response to continued research about flavonoids and other antioxidant compounds could reverse that course.

Which brings up another issue: Can chocolate-lovers give up their sweet milk chocolate for the bitterness of dark?

Keen's answer is ''yes.'' Taste is adaptable, he said. People can learn to enjoy less salty food, for instance, when they need to reduce the sodium in their diet. And they can learn to like a little bitter with the sweet.

''A lot of this is getting the American tongue educated,'' he said.

How to eat chocolate

Eat chocolate after supper when you are full and less likely to overindulge. Remember it's a treat, something extra, and shouldn't replace nutrient-rich fruits and vegetables.

Eat a small amount, in the range of 1 to 2 ounces.

Enjoy small pieces with fruit, which adds nutrients, helps fill you up and satisfies a sweet craving.

Take small bites and let each portion linger in your mouth, savor it and finish it before going on to the next bite.

- Knight Ridder News Service

Got a few extra calories to spend?

Experts say dark chocolate, although high in calories and fat, still can be a healthy choice compared to other treats because of flavonoids' potentially beneficial effects.

Five Dove dark chocolate pieces, 40 grams, 210 calories, 13 grams fat

Four Ghirardelli dark chocolate squares, 43 grams, 220 calories, 17 grams fat

Lindt Excellence dark chocolate, 40 grams, 220 calories, 17 grams fat

Hershey's milk chocolate bar, 43 grams, 230 calories, 13 grams fat

Coca-Cola, 12 ounces, 140 calories, 0 fat

Lay's potato chips, 1 ounce, 150 calories, 10 grams fat

- Knight Ridder News Service