As a measure for the prevention and control of nosocomial infections in medical school students, we examined the students' titers of antibodies to measles, rubella, varicella, and mumps viruses to determine whether vaccination was required. We also analyzed and discussed correlations among antibody titers to the viruses. Subjects were 363 Juntendo University students, ranging from freshmen to seniors. EIA was used to measure IgG antibody titers. Eight subjects (2.2%) had negative titers for measles, 36 (9.9%) for rubella, 8 (2.2%) for varicella, and 10 (2.7%) for mumps. Seronegative subjects were vaccinated against each virus and high seroconversion rates were obtained: 100% for measles and rubella, 67% for varicella, and 89% for mumps. In addition, we used Pearson's test to search for correlations among the antibody titers for each virus. A weak correlation was observed among antibody titers for measles, rubella, and mumps but not for varicella. These results suggest that MMR vaccine might be effective in people with low levels of antibody to measles, rubella, and mumps.