A serum bank maintained for renal transplant recipients allowed for a longitudinal study of antibody responses before and after herpes zoster. Renal transplant recipients without herpes zoster served as controls. Antibody responses to varicella-zoster virus, herpes simplex virus type 1, and cytomegalovirus were measured. The serological responses following herpes zoster were prompt and sustained (in the majority of cases), transient, or not present at all. Zoster without an eruption occurred (apparent only on retrospective chart review) and furnished an explanation for unexplained unilateral pain syndromes in these patients. Asymptomatic rises in titer of antibody to varicella-zoster virus not explained by rises in antibody to herpes simplex virus occurred in both groups. This latter finding points to an unstable relation between virus and host and supports and hypothesis of Hope-Simpson that subclinical release of virus with resulting antigenic stimulation may maintain immunity to varicella-zoster virus. Patients with herpes zoster and controls did not differ in several humoral immune parameters that might have explained the occurrence of herpes zoster. There was no evidence that herpes zoster precipitated renal graft rejection.