Two hundred eleven HIV-seropositive patients with AIDS, AIDS-related complex, or a CD4+ cell count less than 200 x 10(6) were examined for the presence of hepatitis B virus markers during the course of their HIV infection (median follow-up of 18 months; range of 1 to 107 months). Anti-HBs was detected initially in 138 patients (65%). Sixteen patients (8%) were HBsAg positive at entry. Fourteen had chronic HBV infection of whom 12 initially were positive for HBeAg and HBV DNA; 11 remained positive during follow-up, whereas one seroconverted to anti-HBe and lost HBV DNA. Two patients with chronic HBV infection were initially negative for HBeAg and HBV DNA: one later had reactivated HBV replication and one cleared HBeAg following onset of hepatitis D infection. The last two HBsAg-positive patients had resolving acute HBV infection. Six of the 57 patients who initially were negative for HBV markers acquired HBV infection during follow-up. Four of these six patients developed chronic infection whereas two patients had acute subclinical resolving hepatitis. In addition, four patients became HBsAg positive with their last serum samples, possibly indicating reactivation of HBV infection following progressive immunological and clinical deterioration. None of the patients developed clinical symptoms that could be ascribed to HBV infection, and transaminase elevations were only sporadically recorded. It is concluded that acquisition of HBV infections is not infrequent in HIV-seropositive patients with immune deficiency. Furthermore, the course of both previously established chronic HBV infection and newly acquired HBV infection is modified in such patients, whereas reactivation of past HBV infection seems to be a rare event.