ABSTRACT— A total of 308 individuals belonging to ten different ethnic groups in Senegal were investigated. They suffered from primary hepatocellular carcinoma (PHC), liver cirrhosis, chronic hepatitis and other liver diseases, or were healthy controls. Their sera were investigated for the presence of markers of infection with hepatitis B and D (delta agent) virus. Out of 130 clinically diagnosed patients with PHC, 88 had alpha-fetoprotein levels above 100 μg/l, supporting the diagnosis. After clinical examination, 133 subjects were considered to be healthy or to have a liver disease other than PHC. Among these, 83 (31 clinically healthy and 52 with liver disease) had alpha-foetoprotein less than 15 μg/l and were therefore considered not to have PHC. Out of the 88 patients with definite PHC, 74% were positive for HBsAg, whereas out of the 83 subjects without PHC, 50% of those with other liver disease and 26% of the healthy controls were positive. Anti-delta was present in 21% of the patients with or without PHC. It was found in nine different ethnic groups in the country. The present data confirm that HBV is related to the etiology of PHC. The present investigation showed a high prevalence of delta antibodies in patients with PHC, but against the role of hepatitis D infection in the evolution of malignancy is the fact that it was equally common in chronic liver disease without evidence of carcinoma.