Within a three-year period 712 patients with Campylobacter jejuni infection were diagnosed at our laboratory in Helsinki and 524 (72%) were treated as outpatients. More than half (57%) of the patients became infected when abroad, chiefly during holiday trips in the Mediterranean and in East European countries. The risk of acquiring infection was about 250 times greater abroad than in Finland, and it differed considerably from country to country, being highest in Morocco and Tunisia. Among domestic cases the incidence of infection was significantly higher (p less than 0.001) during the summer and autumn months than during winter or spring. Animal contact prior to infection was reported in 59% of domestic and 31% of imported cases, and previous consumption of poultry in 28% and 42% of those from whom information was obtained. Besides diarrhoea (98%), the main symptoms included abdominal pain (87%), fatigue (81%), fever (78%), malaise (70%) and headache (51%). Arthralgia was observed in 19% and arthritis in 2% of patients. The mean duration of diarrhoea was 10.8 days, of fever 2.8 days.