Yuppie alert: Gaithersburg entrepreneur Robert Rosenthal has weighed the market opportunities and come up with what he hopes is the perfect new product -- a hand-held analyzer to measure human body fat.

The device, which carries a $300 price tag and will be on the market later this year, will be marketed to anyone who can afford to get in on the latest health craze of measuring body fat. "California yuppies are buying such products now," Rosenthal said.

The product is being developed as a joint venture between Futrex, a company owned by Rosenthal, and Japan's Kett Laboratories.

Futrex already is marketing a larger version of its hand-held model. Its $1,490 machine, which looks much like a giant calculator, works by beaming infrared light onto the forearm. Fat absorbs some of the wavelengths and the remaining light is picked up by a detector, which then provides customers with a printout detailing their percentage of body fat.

The printout also gives users data on the amount of calories burned by jogging, swimming and other exercise programs, and how many minutes of activity each week would be needed to lose the requisite poundage.

What kind of background does it take to make fat analyzers? Well, another company owned by Rosenthal, Gaithersburg-based Trebor Industries Inc., already makes a variety of machines that use similar infrared technology to measure the nutritional content of food for grain houses, supermarkets, research centers, agricultural universities, and fruit and animal growers. So far, the company has sold 5,000 of the devices at an average price of $10,000 apiece.

"For you and me, we eat McDonalds," Rosenthal said in an interview at Trebor's offices. "But for animals, the animal grower wants to grow his little piggy and have it grow fast and get to market. The more nutritious the feed, the less time the animal takes to grow to the point where it can be harvested."

From analyzing the contents of pig feed, Rosenthal said, it's a fairly short leap to analyzing the fat content of pigged-out yuppies.

Rosenthal has built his empire -- he declines to discuss financial results -- on the fruits of government research combined with some sharp commercial thinking and creative marketing techniques.

He hires college students looking for summer work to research countries and their markets. Then, he chats up foreign ambassadors to make sure they direct traveling dignitaries to his house for lox and bagels.

"They're lonely and sick and tired of hotels," he said. "You always end up with a friendship. It doesn't help if you have a crazy product, but if you have a competitive product, it does."

The result: 70 percent of Trebor's business comes from 22 countries.

Like many entrepreneurs with start-up companies, Rosenthal, 55, began his empire on a shoestring nine years ago after leaving another local technology company.

"I had semiretired and was supposed to be teaching and I convinced my wife to put up a little bit of money to start a company and then I got this terrible disease called entrepreneurial stubborness," he said. "I took three mortgages, I sold my car, and borrowed money from every relative that ever heard of me. ... We have a little jar where we save coins, and when we got down to that jar we finally got the first unit to work."

Rosenthal was able to produce a commercially successful fat measuring product by finding cheap parts for the devices he invented.

For instance, the fat and feed analyzers are based on the infrared light-emitting diodes used in remote-control TV channel changers. By measuring differences in the light as it is transmitted through and reflects off materials, Rosenthal's analyzers can chart fat or feed content.

"What could be cheaper?" he said.