To assess the degree of immune system activation associated with addiction or hepatotropic viruses infection, we examined 60 HIV-negative heroin addicts for the presence of hepatitis B virus (HBV) infection markers, hepatitis C virus antibodies (anti-HCV), various auto-antibodies, and serum levels of soluble interleukin-2 receptors (sIL-2R). In addition, 28 anti-HCV positive patients comprising the disease control group, were also examined. Our results demonstrated a high prevalence of anti-HCV antibodies (61.7% and 90% with 1st and 2nd generation ELISA, respectively). Eighty-seven percent (87%) of the addicts positive for anti-HCV by the latter and 92.8% of the disease control patients, were also positive with 2nd generation recombinant immunoblot assay (RIBA-II). In 88.9% of anti-HCV positive addicts, antibody to C22-3 was the predominant (anti-C33c in 81.5%). Antibodies to C33c and C22-3 polypeptides were also more frequent in disease control group (92.8% and 85.7%, respectively). Anti-HCV antibodies were associated with increased transaminases (ALT or AST, P < 0.05), as well as with longer duration of addiction (P < 0.005). HBV infection markers (HBsAg, anti-HBc only and anti-HBs) were also present in the addicts (5%, 28.3% and 26.7%, respectively). Rheumatoid factors (RF) were detected in 36.7%, antinuclear antibodies (ANA) in 11.7%, antibodies (IgG and/or IgM) against cardiolipin (anti-CL) and double stranded DNA (anti-ds DNA) in 20% and 50%, respectively. RF, ANA, anti-CL and anti-dsDNA antibodies were also detected in the disease control group (32.1%, 89.3%, 28.5% and 28.5% respectively).(ABSTRACT TRUNCATED AT 250 WORDS)