We encountered a case of cytomegalovirus (CMV) retinitis with spontaneous regression in association with an increased number of CD8+ but not CD4+ T lymphocytes in a patient with acquired immunodeficiency syndrome (AIDS). Thus, we examined the number of CD4 and CD8 counts at the diagnosis of CMV retinitis and compared with those of Pneumocystis carinii pneumonia (PCP). All 21 patients with a confirmed diagnosis of PCP (22 episodes) and 14 CMV retinitis patients were included in this study. Although PCP occurred after depletion of CD4 count to below 200/microl, CD8 count at that time varied widely and remained normal in some patients (median: 276.5/microl, range: 133-900/microl). In contrast, as CMV retinitis occurred after further depletion of CD4 count to below 50/microl, CD8 count decreased to below 500/microl (median: 238/microl, range: 43-448/microl) (p<0.05; PCP vs CMV retinitis). The values of the sensitivity and specificity for CMV retinitis obtained at the cutoff point of either 400/microl in CD8 count and 50/microl in CD4 count were similar. When these two cutoff points were combined, the positive predictive value was 46%. Monitoring of CD8 count may prove valuable as an additional predictor of CMV retinitis in patients with AIDS after CD4 depletion.