The purpose of the Study on the Efficacy of Nosocomial Infection Control (SENIC Project) was to evaluate nosocomial infection prevention and control programs in hospitals in the United States. The overall plan was to assess the surveillance and control activities in hospitals in the United States in 1970 and 1976, to measure the change in the nosocomial infection rates from 1970 to 1976 as determined from a carefully conducted retrospective chart review, and to assess the influence of changes in these programs on infection rates after controlling for other important changes that occured during the interval. The SENIC ‘bottom line’ was that 32% of infections that would have occurred in the absence of well-organized infection surveillance and control programs were potentially preventable. However, only 6% of infections were actually being prevented by programs that existed in 1976. The critical components of an effective program were a balance between surveillance and control efforts, one infection control nurse for every 250 beds, a trained hospital epidemiologist, and feedback of surgical wound infection rates to practicing surgeons. In the United States, priorities for nosocomial infection prevention and control efforts include infections caused by emerging pathogens such as coagulase-negative staphylococci, enterococci, and Candida species; infections of the blood stream and surgical wounds; and infections in critical-care units. In addition, there is a critical need for timely analysis and dissemination of surveillance data and for continued training of infection control practitioners and physicians to maximize the effectiveness of prevention and control efforts.