The polymerase chain reaction (PCR) was used to detect hepatitis D (HD) viremia in patients infected with the human immunodeficiency virus (HIV). Nineteen (9%) of 206 such patients, unselected for liver disease or HBV infection, were found prospectively to be infected by HDV. Thirty-one anti-HIV-positive patients were studied by means of PCR, and the results were analyzed according to HDV and hepatitis B virus (HBV) serological status. HDV-PCR was positive in 5 patients. Two had detectable serum HDV antigen. Four patients had anti-HD IgM and IgG antibodies. All these patients were HBs antigen-positive, and 3 were HBV-DNA-positive. All the other patients were HDV-PCR-negative. Statistical analysis suggested more extensive liver damage and immunological impairment in HDV-PCR-positive patients. In this unselected HIV-infected population, HDV-RNA detection by PCR was restricted to HDV infected patients in whom 5/19 were positive. This test permitted direct diagnosis of HDV viremia and will be useful for monitoring HDV infection.