Phenotypic markers were studied in 105 strains of thermophilic campylobacters isolated from human beings, animals and drinking water in Santiago, Chile. The strains were identified as Campylobacter jejuni (n = 49) and Campylobacter coli (n = 56). Biotypes I and II (Lior schema) accounted for 96 % C. jejuni isolates, the other 4% being biotype IV but the two biotypes of C. coli were about equally represented. A total of 28 serogroups (Lior's heat-labile antigens) were identified. Lior 13,9, 79, 2 and 4 were prevalent among the C. jejuni, while Lior 8, 21 and 29/75 were prevalent among the C. coli isolates. These serogroups accounted for 73 % all isolates. The distribution of biotypes and serogroups in patients and asymptomatic persons were similar. Human campylobacters were often resistant to ampicillin (31%) but sensitive to erythromycin and furazolidone. Swine C. coli isolates proved resistant to streptomycin (46%), tetracycline (38%) and erythromycin (15 %). Determination of phenotypic and serological characters provides valuable epidemiological markers in the study of campylobacter infections. © 1990 The British Society for the Study of Infection.