The efficacy and safety of IFN alpha 2a and Thymosin alpha1 combination therapy in patients with chronic hepatitis C were determined. Twelve chronic hepatitis C patients (9 M, 3F), with positive HCV-RNA and histology compatible with chronic hepatitis C were included in this open, prospective study. Each patient received a combination therapy of IFN alpha 2a 3 mU s.c. TIW and Thymosin alpha1 1.6 mg s.c. twice a week for 52 weeks. Up to the present, 11 patients are still being followed-up after the end of 52 weeks' treatment. One patient dropped out after 32 weeks of follow-up due to noncompliance. Responses to treatment were evaluated by measuring serum HCV-RNA levels determined by RT-PCR. and serum amino transferases at the end of 48 weeks of treatment (end of treatment response: ETR). There were 8 naive and 4 previously IFN treated patients with partial response with a mean age of 45.0 +/- 10.1 (mean +/- SD). The mean duration from diagnosis until treatment was 25.1 +/- 22.9 months. The mean AST, ALT, and HCV-RNA levels before treatment were 79.5 +/- 36.8 U/L, 128.3 +/- 68.5 U/L, and 3.9+1.9 x 10(5) copies/ml respectively. Serum AST, ALT, and HCV-RNA levels were significantly lower at week 24 and 48 after treatment compared to before treatment (p<0.05). Of 11 cases, complete HCV-RNA clearance at week 24 was noted in 33.3 per cent, whereas, normal alanine aminotransferase values (ALT < 40 U/L) were observed in 41.7 per cent of patients. Complete HCV-RNA clearance and normal alanine aminotransferase at week 48 were seen in 45.5 per cent of the patients. At the end of week 48, complete response occurred in 4 of 5 naive patients. Minor side effects were observed during treatment with this combination therapy and these included myalgia (33.3%), mild form of alopecia (33.3%), and weight loss (8.3%). In patients with chronic hepatitis C, Interferon alpha 2a and Thymosin alpha1 combination therapy produced a good response rate especially in naive patients with acceptable safety profile. The sustained response will be determined after the completion of follow-up for another 6 months.