OMAHA, Neb. — Fearing bad news as her son suffered with a cough, aches and a sore throat, Donna Bultez found help in the most common of places — her neighborhood grocery store.

Just feet from the beeping cash registers, a few steps behind the frosted-glass door, Bultez was relieved to find that her son Trevor Belmont wasn't suffering from strep throat. That she saved money by avoiding a trip to the emergency room was good news, too.

More and more stores — from small-scale chains like Bultez's local Hy-Vee to megamarkets like Wal-Mart and Target — have started trial runs with in-store medical clinics.

The concept is so new that analysts weren't sure how many clinics exist. They said retailers appear to be trying clinics as a way to increase foot traffic in their stores, rather than rely on the clinics as an entirely new revenue stream.

The ventures are promising enough that America Online founder Steve Case put $500 million into a company that buys stakes in smaller companies that set up the clinics.

Except for a 20-minute wait, Trevor's visit to the Hy-Vee clinic seemed convenient at every turn. His pediatrician was out of his office this day and, without the walk-in service, Bultez might have considered an expensive trip to an emergency room to seek treatment.

"This cost and convenience trend is coming to a head, and that's what is driving this trend. My prediction is that it will move quite rapidly," said Matt Eyring, managing director of Innosight, a Watertown, Mass., consulting firm.

The business model is simple — a medical clinic operated by an outside company, and generally staffed by nurses or physician assistants, offers a limited range of basic tests and treatments at a lower cost than a doctor's office.

Case invested heavily in Revolution Health Group, a company that, among other things, is buying stakes in clinic operators. Its backers and board include former Secretary of State Colin Powell, former Hewlett-Packard CEO Carly Fiorina and former Fannie Mae chairman Franklin Raines.

Seattle-based healthcare analyst Kathleen O'Connor said it's difficult to say how many in-store clinics exist because the trend is so new and it is not clear whether anyone is tracking it. These clinics are different from the stand-alone sites sometimes referred to as a "doc in a box."

The in-store clinics hope to evoke the idea of convenience with their very names — Quick Care at the Omaha Hy-Vee; RediClinic, controlled by Revolution and one of four providers for Wal-Mart; and MinuteClinic, which has 70 clinics in CVS pharmacies, Target Stores and Cub Foods supermarkets.

"We'll certainly grow this business if it makes sense," Wal-Mart spokeswoman Sharon Weber said. "I can tell you the customers have been very pleased."