The prevalence of measles, mumps and rubella antibodies for ages over six months was obtained using a stratified random sample of stored sera submitted in 1988 prior to the implementation of MMR vaccine. Besides reflecting the different vaccination policies for the three viruses the results showed that males display earlier sero-conversion for all three infections and a higher proportion of older males are susceptible. Two-thirds of children aged 6-15 months had antibodies to measles, the majority of which were apparently vaccine induced. However, the possibility that a few children contract natural measles before the recommended age for MMR vaccine cannot be ruled out. A system of continuous sero-surveillance to monitor the effect of MMR vaccine is suggested.