Two medical technologists were appointed as permanent members of a new epidemiology section in the diagnostic microbiology laboratory of a large Veterans Administration Medical Center in the fall of 1989. These positions accounted for 9% of the total microbiology staff and were created on a temporary basis 2 years earlier from a need to have dedicated technical expertise for use in the culture, isolation, and typing of nosocomial organisms. The technologists have evaluated outbreaks due to Clostridium difficile, methicillin-susceptible Staphylococcus aureus, and Serratia marcescens, and have begun work on a methicillin-resistant Staphylococcus aureus (MRSA)-typing scheme. Their major responsibility has been the development and application of molecular biology techniques for the typing of nosocomial isolates, including restriction enzyme analysis of genomic DNA, plasmid profiling with and without restriction enzyme analysis, ribosomal RNA probing of restricted genomic DNA, and selected DNA sequencing of target organisms. Medical supervision rests jointly between the directors of the infection control program and the microbiology laboratory. During their tenure, infections due to C. difficile have dropped from 95 cases per year to 57 cases annually, treatment of MRSA colonization with systemic agents has been curtailed, and a case control investigation involving S. marcescens was avoided. The inclusion of medical technologists in the infection control practice of large medical care facilities, particularly with the availability of molecular epidemiologic techniques and the emergence of increasing numbers of multiply-drug-resistant pathogens, will become an essential component of these programs.