Studies have confirmed HBsAg antigenemia as an important correlate of HIV-1 infections in Nigeria. However, the hepatic pathophysiology and therapeutic implications in antiretroviral regimens are poorly understood. In this study, fifty-four HIV-1 seropositive patients aged 16-47 years (mean age 31.8 years) with CD4 T lymphocyte counts of 148-420 cells/mm3 attending clinics in General Hospital, Ikeja and private medical centres in Lagos Island, Nigeria and forty sex and age-matched apparently healthy controls were serologically examined as carriers of hepatitis B surface antigen (HBsAg) using a particle agglutination assay procedure (Sensitivity 94.5 - 100%, Serodia-HBs.PA, Fujirebio, Inc.). HBsAg was detected in 28 (51.9%) and 5 (12.5%) of the patients and controls respectively ( 2 Mantel-Haenszel = 13.8; P = 0.02). HBV co-infection was found to result in significant (P < 0.05) reduction in total lymphocyte count (1368.6 +/- 53.2 vs. 1590.5 +/- 80.4 cells/ mm3) with 7 of 10 (70%), 18 of 33 (54.5%) and 3 of 6 (50%) HIV-1 patients having < 200, 200 - 350 and > 350 CD4 lymphocyte cells/microl and eliciting HBsAg antigenemia. These patients exhibited 2.9 - 8.6% reduction in CD4 T lymphocyte counts compared to their seronegative counterparts. Although the liver function parameters measured in HIV-1 patients tested were higher than control values, significantly (P < 0.05) elevated liver enzymes: sGOT (44.1 +/- 2.2 vs. 26.2 +/- 2.1 IU/L), sGPT (46.2 +/- 2.4 vs. 23.5 +/- 1.8 IU/ L), and serum bilirubin levels (2.04 +/- 0.18 vs. 1.0 +/- 0.07 mg/ dL) were observed in HBsAg positive HIV-1 patients. sGOT or sGPT activity that was five times greater than the control was observed in 7(25%) and 2 (7.7%) of HbsAg positive and negative HIV-1 patients in whom significant association between decreased total lymphocyte count and measured liver parameters was found. We conclude that hepatitis infection deteriorates liver functions and its investigation in HIV-1 infected patients may be of clino-therapeutic importance prior to antiretroviral therapy administration.