Clinically, acute hepatitis C is an asymptomatic disease in up to 90% of cases. Transaminases fluctuate characteristically. Anti-HCV (RIBA-II) and HCV-RNA (PCR) are diagnostic early in the course of the disease. The risk of chronification is high, exceeding 50% of cases, irrespective of disease transmission (parenterally or sporadic). Alpha-interferon is applicated in pilot-studies to reduce the risk of chronification, with varying results. Chronic hepatitis C is an insidious disease. Again, most cases are asymptomatic. Bilirubin is normal. GPT-activity tends to fluctuate during the course. Anti-HCV and HCV-RNA can be detected in serum. About 20% of cases progress to cirrhosis (and HCC) after a long-lasting disease (20 to 30 years after infection). Alpha-Interferon therapy is successful in about 25% of patients.