What is two inches high, smells like gin and vermouth, and sticks to your refrigerator? Why, a scratch 'n' sniff martini sticker, that's what. And if you hang out with the 5-to-12-year-old set, you may know somebody who has one.

Stickermania is sweeping the country. Not since the Beatles landed 20 years ago has any phenomenon so captured the fancy of prepubescent girls and -- to a lesser extent -- boys. The stickers come on long rolls and are sold in card, gift, and book stores for 5 cents to $1. They carry pictures of hearts, unicorns, ice cream cones, martinis, you name it. Kids are wild about them. Indeed, the fad has reached the point where some retailers have had to develop elaborate security measures to keep eager collectors from raiding their garbage for discarded stickers. At least one elementary school in New Jersey has banned stickers during school hours. Other schools have sought to control the problem by setting aside special sticker periods.

"It's sheer madness," says Lisa Frank, president of a Tucson sticker company that bears her name. "The postman tells us we get more mail than anyone else in Tucson. We must get about 1,000 letters a week from our fans."

Aside from stardom, stickermania has meant soaring revenues and dizzying change for the five or six small companies that have emerged as the most creative, popular, and successful suppliers of the craze. Three years ago, after all, the sticker business scarcely even existed. Most of these companies were doing graphic design work of some sort, with average annual revenues in six figures. Today, the top sticker makers report annual sales on the order of $6 million each, largely from stickers.

The success of the sticker companies, moreover, has come as something of a surprise. "When we first started making stickers [in 1980], we thought we were making them for adults to decorate packages," says Steve Lishansky, director of marketing at Illuminations Inc. in Cambridge, Mass. "It was our retailers who told us that kids were buying them."

Fads are mysterious phenomena, and it is often hard to figure out why one catches on. But in the case of stickers, one person is often credited with launching the craze -- Andrea Grossman, president of Mrs. Grossman's Paper Co. of San Rafael, Calif. "It all started as a favor for a customer," says Grossman. "She wanted some red hearts for Valentine's Day, and she couldn't find any. So we had about 50 rolls printed up and sold them to other stores, too. Every roll sold out."

Grossman was apparently the first person to put stickers on rolls, which made them easy to market, display, and sell. (Previously, decorative stickers came in packages or booklets, which usually sold for a dollar or more.) As it turned out, the rolls also created what one manufacturer terms "the penny-candy effect." Retailers display them on racks near the cashier's counter, and the streamers of colorful stickers catch the attention of children, who can choose the ones they want and buy them for as little as 5 cents each. "These days, there's not a whole lot of things a kid can get for under a dollar," notes John Grimes, president of Cardesign Inc., a sticker company in Oakland, Calif.

Perhaps inevitably, kids have begun to collect stickers, giving the industry a certain momentum. Grimes says he recently got a letter from a 12-year-old girl with a collection of 15,000 stickers. Collections of 2,000 to 5,000 stickers are relatively common. For obvious reasons, the companies are doing all they can to encourage the trend. Grimes has hired a full-time editor to put out a newsletter called Sticking Together and is launching a national sticker club. Grossman has diversified into albums, books, and other sticker-collecting paraphernalia.

But what will they do if the fad fades? "We're coming out with a number of different stationery lines," says Lishansky of Illuminations. "But stickers will be around for a while. Like wall posters, they might just start out as a rage, then stabilize into a reliable cash cow." A four-color, glossy, scratch 'n' sniff cash cow, no doubt.