Sera (-70 degrees C) from 66 patients treated with interferon (3 million units three times a week for 6 months) were assayed with a quantitative polymerase chain reaction (sensitivity<or =100 copies per milliliter). Evaluations were made at baseline, during treatment at weeks 1, 2, 4, 12, and 24, and at follow-up week 48. Biochemical response was defined using standard alanine aminotransferase criteria