Anecdotal evidence suggests that innovative medical devices often arise from physicians' inventive activity, but no studies have documented the extent of such physician-engaged innovation. This paper uses patent data and the American Medical Association Physician Masterfile to provide evidence that physicians contribute to medical device innovation, accounting for almost 20 percent of approximately 26,000 medical device patents filed in the United States during 1990-1996. Moreover, two measures indicate that physician patents had more influence on subsequent inventive activity than nonphysician patents. This finding supports the maintenance of an open environment for physician-industry collaboration in the medical device discovery process.