In review of the ongoing protocol for the treatment of Wegener's granulomatosis with cyclophosphamide at te National Institutes of Health, an increased incidence of herpes zoster infection was noted. There were a total of nine episodes in seven of a total of 65 patients with a 255 patient year follow-up. The infections occurred while the patients were in complete clinical remission during immunosuppressive therapy. Cutaneous dissemination was noted in two episodes, but no visceral or central nervous system involvement was noted despite continuation of immunosuppressive therapy. The major causal factor of the increased incidence of herpes zoster appeared to be the cyclophosphamide therapy.