Bivalent virus vaccine, containing rubella TCRB-19 strain and mumps NK-M46 strain (MR vaccine), was administered to a total of 95 healthy children who had already received measles vaccine or had been infected with wild measles virus. The seroconversion rates for rubella and mumps viruses in subjects having no antibody to rubella or to mumps virus were 99%(75/76) and 97%(63/65), respectively, at 6-8 weeks after vaccination. The seroconversion rates for both rubella and mumps in vaccinees initially seronegative to both viruses were 95%(56/59). Immune responses after MR vaccine injection were comparable to those after administration of monovalent rubella or mumps vaccine. Clinical reactions observed in some subjects who received MR vaccine were mild fever (3.6%), examthem (8%), lymphadenopathy (1.8%), and swelling of the parotis region (1.8%). MR vaccine could be simultaneously injected with varicella vaccine at the opposite site producing no adverse effect on immune response. Our results indicate that MR vaccine is a safe and effective vaccine, especially for children who have had wild measles or who have received measles vaccine.