The hepatitis C virus is a positive stranded hepatotropic RNA virus. We describe a method of detecting positive and negative strands of hepatitis C viral RNA using the polymerase chain reaction. We tested serum and liver tissue from nine patients with chronic hepatitis C. The positive RNA strand of HCV was detected in the sera and livers of all nine, the negative strand was detected in the livers of eight (89%), and in the sera of five (55%). Titers of both strands of HCV RNA were determined by serial endpoint dilutions. The amount of the negative strand in the serum and liver was usually 10-100 times less than the positive strand. Predigestion of serum with ribonucleases did not alter the detection of the negative strand. This suggests that the negative strand found in the serum may be protected from digestion by being associated with virions.