The only strict exclusion criterion will be active therapy with interferon. The basis for this exclusion was the findings from a retrospective analysis of a recent trial of recombinant human alpha interferon as therapy of chronic hepatitis B. In that study, the "response rate" or rate of clearance of hepatitis B virus with alpha interferon therapy was lower among patients who underwent lymphapheresis during therapy (48 percent) (p less than .01). Lymphapheresis performed before treatment did not seem to affect the outcome of interferon therapy. These findings were unexpected but have led us to avoid both plasmapheresis and lymphapheresis in patients receiving alpha interferon therapy. The reasons why lymphapheresis might interfere with a response to alpha interferon are to known, but probably relate to the importance of an intact, healthy immune system in the process of recovery from a chronic viral infection.