A clinical and serological investigation of an epidemic due to Campylobacter jejuni in a community with a population of 1026 is presented. Altogether, 22 faecal samples from 27 patients were positive, with serotypes O 2 (n = 21) and O 6, 7 (n = 1) being identified. Serotype O 19, 21 was isolated from drinking water which had been consumed by 89.5% households answering a questionnaire, thereby indicating an attack rate of 66.5% (i.e. 680 persons). Mean duration of illness was 6.5 +/- 4.6 days. Diarrhoea (82.3%), abdominal pains (62.8%) and fever (41.8%) were the most common symptoms. Acute stage samples of serum from Campylobacter-positive patients had lower concentrations of IgG antibodies against the most common serotype (O 2) than against serotype O 6, 7 (P = 0.05), which had previously been implicated in epidemics in the region. More than 80% samples drawn after 1-2 weeks of illness were positive for either IgA, IgM or IgG antibodies to serotype O 2 with a dominance of IgA. In the convalescent group (n = 24), serum from only one patient who developed a long-lasting reactive arthritis had antibodies to all serotypes.