Thirty-two patients with Hodgkin's disease and 12 normal donors were studied for their in vitro lymphocyte responsiveness to a membrane-associated varicella-zoster (VZ) antigen. When compared to the normal donors, patients with Hodgkin's disease in whom radiotherapy was recently completed and those with active, recurrent disease had markedly impaired cell-associated immunity to VZ antigen. In addition, there was a suggestion that patients in long-term remission who had received primary combined modality therapy (radiotherapy plus chemotherapy) had an impaired response when compared to normal persons or to patients who had received single modality therapy. Newly diagnosed, untreated patients with Hodgkin's disease did not differ significantly from normal persons as a group but two of six were unresponsive to the VZ antigen whereas all normal subjects were responsive. Most patients in remission for at least one year following therapy had normal in vitro responsiveness. In two patients herpes zoster developed after the demonstration of absent in vitro lymphocyte reactivity to the VZ antigen.