A total of 44 children aged between 15-18 months were randomly vaccinated either with a new measles-mumps-rubella (MMR) vaccine (Priorix(R), SmithKline Beecham) or a commercially available MMR vaccine (MMR-II(R), Merck) to compare the reactogenicity and immunogenicity. No local symptoms or fever was reported. Seroconversion rates of the study vaccine were 100, 95 and 100 percent for measles, mumps and rubella, respectively. The seroconversion rates for the control vaccine were 100, 94.7 and 95.5 percent, respectively. The geometric mean titers (GMT's) for the study and control groups were 1695, 95, 58; and 2198, 1183 and 47; respectively.