A combined vaccine against varicella and measles-mumps-rubella made by mixing two commercially available products (Varilrix and Pluserix SK-RIT) has proved to be only partially successful in early trials. Although the seroconversion rates with the MMR components were comparable with those usually achieved, the varicella take was depressed to 77%. A new low dose measles-mumps-rubella vaccine was prepared in which the measles virus content was reduced to 1/5 and the mumps virus content to 1/8. Commercial varicella vaccine was added to the low dose MMR vaccine. The seroconversion rates for measles was 98.2%, for mumps 100%, for rubella 99.4% and for varicella 98%. This product seemed to be well balanced in respect of a possible interference between the four different virus vaccine strains.