Four cases of diarrhea due to enteropathogenicEscherichia colideveloped in a nursery for premature infants where no diarrheal disease had occurred for several months. Rectal swabs of the 36 infants and 32 personnel in the nursery were examined by standard culture methods and by the fluorescent antibody technique. Another 5 infants and 1 student nurse were found by fluorescent antibody staining to be colonized with the same organism, but cultures from feces were positive in only 2 of the colonized infants. The epidemic was controlled by isolating infants who harbored the organism, removing the nurse-carrier, and treating all infants with neomycin sulfate. The specificity, sensitivity, and rapidity of fluorescent antibody staining indicate that this method may be more useful than standard culture methods in epidemiological investigations.