Between March 1994 and March 1996 we studied transmission routes and clinical courses in eight patients with sporadic acute hepatitis C (two men, six women). Of the eight patients, three were treated for another illness 1-2 months before the onset of hepatitis, one was a parenteral drug abuser, one had an accidental needlestick injury and two had sexual contact with a partner with chronic hepatitis C virus (HCV) infection. Clinical courses included four women whose HCV RNA and alanine aminotransferase (ALT) became persistently negative without treatment, and four men and two women with the same results following interferon (IFN) treatment. It is thought that IFN therapy may prevent the progression to chronic liver disease. Results from this study might be useful in the future management of patients with sporadic acute hepatitis C.