During a 4-month period during the summer of 1985, campylobacters were isolated from 338 (16.3%) of 2080 patients with acute diarrhoea attending the University Hospital of Infectious Diseases in Zagreb. Of these isolates 220 (64.1%) were Campylobacter jejuni and 118 (34.9%) were C. coli. The patients were drawn from three residential zones in and around Zagreb: inner city, peripheral city and rural. Incidences of campylobacter diarrhoea ranged from 71 per 100,000 per year in inner city residents to 99 per 100,000 per year in the rural residents. Most infections were in young children; the incidence in infants ranged from 800 to 2500 per 100,000 per year in the inner city and rural zones respectively. The isolation rate from faecal specimens of infants from the rural zone was 61%. The ratio of isolation rates in males and females (all ages) was 1.1:1, but in infants it was 0.7:1 and in patients over the age of 65 years it was 0.4:1. The incidence of C. coli in the rural zone was four times that in the inner city and twice that in the peripheral zone. This survey shows that campylobacter infection in Zagreb has distinctive epidemiological features. The transmission of infection appears to be midway between that found in industrialized and developing countries, and there is an unexplained excess of C. coli infection.