Changes in interferon receptors on peripheral blood mononuclear cells from patients with chronic hepatitis B being treated with interferon. We studied the binding of 125I-labeled human interferon-alpha to peripheral blood mononuclear cells and the activity of 2',5'-oligoadenylate synthetase in peripheral blood mononuclear cells obtained from 21 patients with chronic hepatitis B who were treated with human interferon-alpha or interferon-beta. Fourteen patients were given interferon daily for 4 wk. Interferon receptors per cell decreased to about 50% of baseline but increased to baseline by 2 wk after therapy ended. The activity of 2',5'-oligoadenylate synthetase rose about fivefold during therapy, decreasing to baseline by 1 wk after the end of therapy. The seven other patients were given interferon daily for 2 wk, no interferon for 2 wk and then interferon daily for 2 wk more. During both periods of therapy on this schedule, interferon receptors decreased to about 50% but returned to baseline 1 wk after the interferon was stopped. The activity of 2',5'-oligoadenylate synthetase increased about fivefold during both the first and second periods of therapy and decreased to baseline 1 wk after interferon was stopped. Close negative correlation existed between the number of interferon receptors and the 2',5'-oligoadenylate synthetase activity. The results of interferon therapy could not be predicted by either the numbers of interferon receptors before therapy or by the decrease in this number during therapy. 