To evaluate the prevalence of hepatitis C virus infection in northwest China, 179 chronic liver disease patients in this area were examined for antibody to hepatitis C virus core protein (anti-HCVcore). This antibody was found in only 5 (14 percent) of 37 chronic non-A, non-B liver disease patients, in 11 (16%) of 67 asymptomatic hepatitis B virus carriers, and in 20 (27%) of 75 chronic hepatitis B patients. High titers of anti-HCVcore (cut off index > 2) were observed in 3 (60%), 5 (45%), and 9 (45%) of the anti-HCVcore-positive cases of these groups, respectively. We further investigated the seroprevalence of antibodies to hepatitis B virus in the 37 chronic non-A, non-B liver disease patients. All 5 anti-HCVcore-positive cases were positive for a hepatitis B virus marker, with only 44% (14/32) of the anti-HCVcore-negative patients (P < 0.05). Based on these findings, it is concluded that the prevalence of hepatitis C virus infection in chronic non-A, non-B liver disease is unexpectedly low in northwest China and that hepatitis B and C viruses seem to have a similar mode of infection in that area.