The prevalence of antibody against hepatitis C virus (anti-HCV) and five hepatitis B virus markers (HBVM) was measured in 176 Chinese drug addicts, of whom 23 were AIDS patients. Of 176 drug addicts, 147 were members of ethnic minorities while 29 were Han, the majority ethnic group. The total prevalence rates of anti-HCV and HBVM were 35·8% and 50·6% respectively, significantly different (P<0·01). Anti-HCV and HBVM were together found in 22·7%. Similar prevalence rates were found among the different ethnic groups. Among the ethnic minorities, there was a significantly higher prevalence rate of anti-HCV in intravenous drug addicts (IVDA, 51·1%) than in oral drug addicts (20·3%). Furthermore, the prevalence of anti-HCV was significantly higher in needle-sharing abusers (60·4%) than in non-needle sharing ones (37·1%, P<0·05). The prevalence of HBVM was also significantly higher in needle-sharing abusers (69·8%) than in non-needle sharing ones (34·3%). Prevalence of HBsAg was significantly higher in drug abusers with AIDS (47·8%) than in IVDA only (16·1%). The anti-HCV positive rates among ethnic minority people were: for the Yi people 69·2%, the Hui 55·6%, the Bai 53·9%, the Dai 26·8% and the Wa 23·1%. No obvious difference was identified for HBVM. The prevalence rates of HCV, HBV and HCV+HBV in IVDA showed no significant difference (P>0·05) between the two regions. HIV, HCV and HBV infections may promote each other and be related to needle-sharing behaviour in drug abuse and to different subcultures and living habits.