In the villages of Fiji, apart from Viti Levu, rubella is a disease occurring solely in widely spaced epidemics. Some villages may not be infected for over 20 years and will then contain substantial numbers of susceptible women of child-bearing age. Evidence is produced that haemagglutination-inhibiting (H.I.) antibody to rubella is very long lasting in Fijians. The infectivity of the virus is discussed and it is suggested that, on the average, 50 % of susceptibles are infected in a Fijian village during a rubella epidemic, but there are large variations.