Gene expression of interleukin 12-receptor beta2 chain mRNA in peripheral blood mononuclear cells (PBMCs) was examined in patients with chronic hepatitis C (n=7) and in healthy control subjects (n=6) by semi-quantitative RT-PCR. The level of interleukin 12-receptor beta2 chain mRNA was higher in patients with chronic hepatitis C than in healthy subjects (P=0.032). The level of interleukin 12-receptor beta2 chain mRNA had a weak correlation with the ratio of Th1 to Th2 populations (r=0.714, P=0.020). There was a tendency for the level of interleukin 12-receptor beta2 mRNA to increase both in chronic hepatitis C (P=0.109) and in healthy volunteers (P=0.144) after the incubation of PBMCs with interferon-alpha in vitro. During interferon-alpha administration to the patients with chronic hepatitis C, the level of interleukin 12-receptor beta2 chain mRNA in PBMCs was increased in all four cases. Although this is a preliminary study with a small sample size, our results suggest that the level of interleukin 12-receptor beta2 chain mRNA is higher than normal in patients with chronic hepatitis C and can be further enhanced by interferon therapy.