Outbreaks of measles, mumps and rubella have occurred recently despite long-standing mass immunization with MMR. Antibody titres for measles, mumps and rubella of 160 students (17-23 years) with proof of at least one MMR-vaccine were studied according to the number of MMR-vaccines received. The proportion of subjects with positive antibody titres was significantly higher in those who received two vaccines against measles (77.1% versus 58.7%, p=0.05), mumps (67.5% versus 55.6%, p=0.009) and rubella (99.2% versus 71.4%, p=0.008). Comparable significant trends were seen for GMTs for measles and mumps. A similar non-significant trend was noted for rubella.