In view of the ethnic and geographical peculiarities of the French department of Martinique and of the endemic character of hepatitis in tropical countries, we studied the prevalence of infections with hepatitis A, B and delta viruses in that region. A group of 10,109 blood donors and a group of about 100 patients were selected on account of their liver symptoms. As regards hepatitis A, the study of the 2 groups was completed by a sero-epidemiological survey of 509 children and teenagers aged from 1 to 18 years. The prevalence of the HB antigen among blood donors was 1.3 per cent, i.e. about 10 times higher than in Europe and 7 times lower than in hyperendemic tropical areas. It was 2.5 times higher in the male than in the female population; 84 per cent of HBs-positive donors had anti-HBe antibodies, 9 per cent had HBe antigen and 7 per cent had neither one nor the other. This distribution is coherent with a population of symptomless carriers. The prevalence of anti-HBs-positive sera was 34 per cent as against 70-95 per cent in highly endemic countries and 4-20 per cent in Europe; 1.9 per cent of the HBs donors studied and 8.8 per cent of the patients had anti-delta antibodies; 11 of the 13 anti-delta-positive subjects had anti-HBe antibodies and 2 had neither HBe nor anti-HBe. Between the ages of 1 and 3 years very few anti-HAV-positive subjects were observed. From 3 to 10 years, the percentage of seroconversions increased moderately. Between 10 and 20 years, the number of positive cases increased considerably reaching 67 per cent at 20 years and 100 per cent at and above 45 years. Among the patients, 97 were positive for IgG (96 per cent) and only 5 for IgM (4 per cent).