We conducted a serological and questionnaire study of 755 US Merchant Marine Academy cadets (aged 16 to 29 years) and their parents to determine the cadets' susceptibility rate to measles and rubella and to see if there was any difference in the accuracy of cadet and parental histories of previous infection and vaccination. Approximately 4% of the cadets were susceptibility. We also determined the costs and the effectiveness of three alternative strategies for vaccinating susceptible adolescents and young adults: (1) vaccinating all persons regardless of past history; (2) serologically screening all persons and vaccinating only those who were susceptible; and (3) vaccinating all individuals who do not have physician-documented proof of proper vaccination, past infection (measles only), or serological immunity. The cost savings among the three alternatives are dependent on the proportion of potential vaccinees with records available for review and must be balanced against the proportion of susceptible persons protected by each alternative. We also found that a combined vaccination program for both measles and rubella is less costly than a program aimed at providing immunity to only one of the two diseases.