During a three-month period in 1971, there were 39 persons in Utah who contracted tularemia. Twenty-eight of the 39 cases (72%) stemmed from bites of the deerfly (Chrysops discalis). Field surveys indicated the occurrence of a tularemia epizootic among rabbits during the epidemic period. Cultures were taken from animals and insects in epidemic areas and Francisella tularensis was isolated from both deerflies and rabbits. Although cultures of mosquitoes and gnats were negative, there was indirect evidence that one of these species may have transmitted tularemia to seven patients.