The prevalence and serological features of hepatitis delta virus infections were studied in a French population of chronic, non-drug addict, hepatitis B surface antigen carriers: 42 male homosexual patients were compared to 30 nonhomosexuals (20 who evidently had not been exposed to any of the usual hepatitis B virus-hepatitis delta virus risk factors and 10 hemodialyzed patients or kidney allograft recipients). Six of the 42 male homosexuals (14.3%) had at least one serological marker of hepatitis delta virus infection (hepatitis delta antigen, total and/or IgM anti-hepatitis delta antibodies). Serological follow-up was obtained for five of these patients over several months and confirmed the chronicity of the delta infection in at least four of the five subjects. Hepatitis delta antigen and hepatitis delta virus RNA were found in the liver and in the serum, respectively, of four of the five tested patients. Hepatitis B virus DNA was negative in the serum of five of the six hepatitis delta virus-positive homosexuals vs. only eight of 35 hepatitis delta virus-negative homosexuals (p less than 0.02). Human immunodeficiency virus was negative in all of the nonhomosexuals; its prevalence did not differ between the hepatitis delta virus-positive and -negative homosexuals: three were human immunodeficiency virus-positive among the six former vs. 15 among the 36 latter. Human immunodeficiency virus positivity was without obvious influence on hepatitis B virus replication, since among 35 hepatitis delta virus-negative homosexuals hepatitis B virus DNA was found in 80% of the human immunodeficiency virus-positive individuals and 70% of those who were human immunodeficiency virus-negative.