The Food and Drug Administration's recent guidance on how it might regulate mobile health applications used by physicians and consumers will affect only a small portion of the apps on the market, the agency said. However, the FDA's expanded regulation of device-related software will affect device manufacturers and the growing number of firms marketing health apps for smartphones and tablets. "The majority of the folks who I've been dealing with do fall within the scope of that guidance document," said Bradley Thompson, a New York attorney specializing in medical device regulation.