An interstate outbreak of hospital-associated infections due to Salmonella derby was first recognized in April, 1963. Between March 1 and Aug 12, 1963, 822 isolations of Sal derby were made from patients, staff, or employees of 53 hospitals in 13 states. Epidemiological investigations indicated that the organism had been introduced into the hospitals by a common source involved in interstate movement. Raw or undercooked eggs were implicated as the common source vehicle of infection. Extensive secondary spread of infection, presumably person to person, has more recently become a major problem in several institutions. Studies to define the mode of spread of secondary infections are currently in progress.