AIMS/BACKGROUND: Recent evidence suggests that spontaneous clearance of hepatitis C virus (HCV) may be associated with the HLA DQB1*0301 allele but there is still some debate over the role of other alleles and HLA haplotypes in HCV infection. As this may best be resolved by studying genetically different populations, we have investigated HLA class II-encoded susceptibility and resistance to HCV infection in a relatively sedentary population of patients from northwestern Poland. METHODS: The distributions of HLA class II DRB1, DQA1, DQB1 and DPB1 alleles were determined by standard PCR-protocol in 129 unrelated patients with chronic hepatitis C (anti-HCV and HCV-RNA positive) and 103 healthy unrelated racially-matched control subjects. Fifty-five patients were treated with alpha-interferon (5 MIU thrice weekly for 6 months) out of whom 29 showed a complete response and 26 were non-responders. RESULTS: A significantly reduced frequency of the DQB1*0301 allele in the patients was observed (24.0% vs. 38.8%; p=0.015). Additionally, two different DR-DQ haplotypes were found to be associated with chronic HCV infection: DRB1*1501-DQA1*01-DQB1*0602 (24.0% vs. 12.6%; p= 0.027) and DRB1*0701-DQA1*0201-DQB1*02 (31.8 vs. 12.6%; p=0.0006), the latter difference being most pronounced in those patients who responded to alpha-interferon treatment (41.4% vs. 12.6%; p=0.00048). CONCLUSIONS: The results confirm the negative association between chronic HCV and DQB1*0301 and identify two novel genetic associations. In particular, the DRB1*0701-DQA1*0201-DQB1*02 haplotype is associated with both chronic infection and response to alpha-interferon. Interestingly, the same haplotype is reportedly associated with non-response to hepatitis B vaccination.