A total of 915 normal children without a history of varicella were immunized with a live varicella vaccine (Oka strain) between 1978 and 1982. As clinical reaction after vaccination, fever and or a slight rash was observed in only 10 children. A serological response was observed in all 524 children examined. Of the 854 children who could be followed, 602 children had contact with varicella patients, but extremely mild varicella with a rash developed in only 10 of them. Mild zoster occurred in one child who was admitted to hospital with mycoplasma pneumonia.