Samples of peripheral blood lymphocytes (PBMC) were serially obtained from 30 patients with herpes zoster (HZ) and 10 patients with chickenpox (CP). Cells were assayed for NK-cell function and for the expression of surface membrane antigens which identify T-cell and NK-cell subsets. During the acute phase of disease (< 7 days from onset), PBMC from patients with HZ had low proportions of T-helper (CD 4+) cells and a large number of T-suppressor (CD 8+) cells, resulting in a low T-helper/T-suppressor ratio. There was an increased percentage of nonspecific suppressor cells (CD 8+-CD 11+ cells) and increased expression of HLA-DR determinants on both CD 8+ and CD 4+ cells. The NK activity was depressed with no concomitant decrease in NK cells (CD 16+ or Leu 7+ cells). In the early convalescing phase of disease (8-14 days), there was a significant increase in CD 16+ cells and increased expression of HLA-DR on these cells, correlating with increased NK activity. In the late recovery phase (> 14 days), NK activity and levels of T-cell subpopulations were normal with the exception of increased CD 4+ cells and, consequently, of the helper/suppressor ratios. In the acute phase of CP (< 7 days), the T-cell imbalances were similar to those encountered with HZ patients. Expression of HLA-DR on CD 8+ and CD 4+ cells was also increased. However, in contrast to HZ, the number of CD 8+ cells coexpressing CD 11 was not increased. In the early phase of CP, there were also increased numbers of CD 16+ cells, some of which coexpressed HLA-DR. NK activity was also augmented. No deviations from normal values were observed in the recovery phase of CP.