Hepatitis C viral load, genotype and/or staging of liver fibrosis are known to be factors for predicting response to interferon(IFN) therapy in patients with chronic hepatitis C. The aim of this study is to investigate if human leukocyte antigen(HLA) typing is related to the response to IFN therapy. The seventy six Japanese patients were studied and categorized into two groups: 46 patients with chronic hepatitis C (Group A) and 30 with liver disease unrelated to HCV infection(Group B). In addition, 39 patients who were treated with IFN were classified into complete responders(CR) and non-complete responders (NR). There was not any differences in HLA typing between group A and B, but the frequency of HLA class I B51(5) was higher in CR than in NR patients(p = 0.045). When restricted to those who had low viral load(under 10(55) copies/ml) and genotype 2a or 2b, HLA class I CW1 was found in 7 responders(70%) and in 1 non-responder(14%) (p = 0.023). HLA class II DR9 was not found in responders but in 3 non-responders(p = 0.022). These preliminary results suggest that HLA types may be related response to IFN therapy in patients with chronic hepatitis C.