We analysed the expression of interferon (IFN) alpha/beta receptor mRNA in the liver of patients with chronic hepatitis C and examined the relationship between the expression of this receptor gene and the level of hepatitis C virus (HCV)-RNA as well as the response to 16 weeks of 6 x 10(6) units IFN. The mean level of IFN alpha/beta receptor mRNA in patients with chronic HCV infection (expressed as delta cycle; 10.8 +/- 1.9 (mean +/- SD); n = 39) was significantly higher than that of control subjects (9.4 +/- 0.5; n = 6; P < 0.01). There was a significant negative correlation between the level of IFN alpha/beta receptor mRNA and serum HCV-RNA in 39 patients with chronic hepatitis C (R = -0.546; P < 0.01). The mean level of IFN alpha/beta receptor mRNA in six patients who showed a complete response to IFN therapy (12.3 +/- 1.6) was higher than that of 15 patients who failed to respond to therapy (10.1 +/- 1.5; P < 0.01). Our results are consistent with the suggestion that the anti-viral activity of IFN depends on the level of the IFN alpha/beta receptor on hepatocytes in patients with chronic hepatitis C.