Because of increasing incidence Of mumps in a cohort of underimmunized young adults and the concern about the impact of this disease on the USAF recruit population, two studies were undertaken. These studies took a retrospective look at mumps in the active duty population, a cost analysis of immunizing all or only susceptible individuals, the actual antibody response in a group of 276 recruits in basic training, the demographic patterns of susceptibilty and the types of previous immunization documentation. The conclusions were that the numbers of new mumps cases per year did not justify immunizing all recruits or screening for mumps antibodies and only immunizing known susceptibles.