The importance of C. jejuni as an aetiological agent of childhood diarrhoea was investigated at an urban children's hospital in Dhaka over a period of 1 year. C. jejuni was isolated from 25.5% of 102 diarrhoeal patients compared to 8.6% of 93 age and sex-matched healthy control children studied (P less than 0.002). The organism was isolated as a single pathogen in 17.6% of diarrhoeal patients. No C. coli was detected. The infection rate was significantly higher (P less than 0.05) amongst children up to 1 year of age (32.8%) compared to those aged over 1 year (15.9%). The clinical features of the majority of Campylobacter-positive cases resembled toxin-mediated secretory type diarrhoea. A fourfold rise of antibody titre against autologous Campylobacter strains was observed in the convalescent sera of Campylobacter-positive cases. The findings strongly suggest that C. jejuni is an important aetiological agent of childhood diarrhoea amongst Bengali children and therefore should be looked for in diarrhoeal illness.