Thrombocytopenia is commonly seen in patients with cirrhosis. Both splenomegaly and inadequate thrombopoietin (TPO) production by the cirrhotic liver are responsible for thrombocytopenia. In addition, thrombocytopenia is frequently observed in chronic hepatitis patients who received interferon therapy, and may even lead to the discontinuation of treatment. The aim of this study is to evaluate the clinical significance of the changes of platelet counts and serum TPO levels in chronic hepatitis C patients treated with different doses of consensus interferon (CIFN). Data from 75 chronic hepatitis C patients who received subcutaneous injection of either CIFN 9 (25 patients) or 3 &mgr;g (26 patients) or placebo (24 patients), three times a week for 24 weeks, were analyzed from a randomized controlled study. All patients received a 24-week observation period after the end of the treatment. The results showed a significantly higher degree of decrease in platelet counts and elevated serum TPO in patients receiving CIFN 9 or 3 &mgr;g as compared with placebo at week 12 and week 24 of treatment, respectively. These changes were more obvious in patients receiving CIFN 9 &mgr;g than in patients receiving CIFN 3 &mgr;g. However, both the decrease of platelet counts and elevated serum TPO levels returned to the baseline values after stopping CIFN therapy. Lower hepatic fibrosis score, lower pretreatment serum HCV RNA level, genotype non-1b infection and patients with sustained response to CIFN were manifested with higher degree of serum TPO elevation in response to the CIFN-induced thrombocytopenia. Multivariate logistic regression analysis showed that an age of less than 45 years and a serum TPO level elevation greater than 50% of baseline level at week 12 of CIFN treatment were significantly independent predictors associated with the sustained response to the CIFN treatment. In conclusion, the changes of platelet counts and serum TPO levels in chronic hepatitis C patients during CIFN therapy were reversible, and the degree of changes were more prominent in higher doses of CIFN treatment. The serum TPO response to CIFN-induced thrombocytopenia may serve as a marker for the degree of liver fibrosis, and also as a parameter for predicting therapeutic response.