In a year long prospective study of diarrhoea in children under 2 years of age in Soweto, South Africa, Campylobacter jejuni was isolated in 18 of 60 children under 9 months of age with diarrhoea, compared with 4 of 60 age matched controls. In the older children, 16 of 51 children with diarrhoea and 17 of 51 control children excreted this organism in their faeces. These results indicate a change in susceptibility to C jejuni in children over 9 months of age. Campylobacter enteritis in the young children was usually mild, without macroscopic blood in the faeces, and prolonged excretion of the organism after acute attacks was not infrequent. Breast feeding did not seem to protect against colonisation with C jejuni.