Two hundred eighty-five isolates of Campylobacter jejuni-Campylobacter coli from children with gastroenteritis at The Hospital for Sick Children (Toronto, Canada) over a three-year period were biotyped by the hippurate hydrolysis test and serotyped on the basis of thermostable, soluble antigens by the passive hemagglutination technique. Hippurate-negative strains (C. coli) were only 3.2% of the isolates. Ninety-seven percent of the isolates were serotypable with 55 antisera. About half of the strains belonged to one of four serotypes (2, 4, 3, or 1); about three-quarters belonged to one of 10 serotypes. Serotype 2 was consistently the commonest serotype in each of the three years of the study, accounting for 15%-20% of all isolates tested.