As part of the first two phases of the SENIC Project (Study on the Efficacy of Nosocomial Infection Control), information was collected from the heads of the infection surveillance and control programs (ISCPs) in U.S. hospitals. The data were analyzed to describe these respondents and to determine whether differences among them were related to their areas of professional training or to characteristics of the hospitals where they were located. The findings indicate that the ISCP heads constitute a very heterogeneous group, with substantial differences in age, professional training (40% are pathologists), characteristics of their medical practices, memberships in professional organizations related to infection control, time spent in ISCP activities, approach to epidemiologic problems, and opinions on the preventability of nosocomial infections and the seriousness of infection problems in their hospitals. These differences are related strongly to the ISCP heads' professional training, size of hospital, and, to a lesser extent, medical school affiliation, but there is little evidence that the differences are related to regional or urban-rural location or type of ownership of the hospitals. The average ISCP head estimates that about half of all nosocomial infections are preventable, but these estimates vary inversely with tenure in the position and the tendency to approach a clinical problem epidemiologically.