We examined the process of accruing healthy control subjects for biomedical research on brain function. Of 1670 responders to newspaper advertising, 23.1% were uninterested when learning more about the studies, and 50.9% of those remaining were found by structured telephone screening to meet exclusionary criteria for having a history of psychiatric, neurologic, or medical disease that might affect brain function. Of 312 volunteers passing the telephone screening who came to an in-person evaluation by a physician and agreed to participate, 49.7% were found to meet exclusionary criteria, and only 157 were admitted to the study. This underscores the importance of attending to the issue of screening and assessment of "normal volunteers." Alternative strategies should be considered for enriching the pool.