New molecular biology techniques recently identified hepatitis C virus (HCV) as the major cause of non-A, non-B hepatitis. Serologic assays for HCV specific antibodies are a significant advance, but they require cautious interpretation due to problems with the tests' sensitivity and specificity. Patients with suspected HCV infection should be thoroughly evaluated to verify the presence of infection, to exclude other forms of chronic liver disease, and to determine the extent of liver damage prior to considering treatment.