The presence of hepatitis B virus (HBV) serological markers have been investigated in 101 Lebanese patients (69 men, 32 women; mean age 32.7 +/- 1.7 years) infected with human immunodeficiency virus type 1 (HIV-1). Seven patients (6.9%) were HBsAg carriers compared with 54 patients (53.5%) who had no evidence of exposure to HBV infection. Twenty-four patients (23.8%) had anti-HBc alone as a serological marker compared with four patients who were positive for anti-HBs alone and 12 patients (11.9%) who were anti-HBc and anti-HBs-positive. Occult HBV infection (presence of HBV DNA in the absence of HBsAg) is found to be relatively high (28.7%) in HIV-infected Lebanese patients and the overwhelming majority (83.3%) of those who were positive for anti-HBc alone had a detectable HBV DNA in their serum. However, none of our HIV-positive patients with occult HBV infection had abnormal alanine aminotransferase level, which also raises the question as to whether occult HBV plays a role in the aetiology of liver disease in HIV-infected patients. Further, studies on the association between HBV DNA levels and markers of liver function in addition to data on liver biopsy would help in answering this question.