Thirteen patients maintained on long-term hemodialysis were studied with respect to their serum zinc concentration and T-lymphocyte response to phytohemagglutinin. Six patients demonstrated depression of T-cell mitogen response, while seven patients demonstrated a normal response. The mean serum zinc concentration of the patients with abnormal response was lower than those patients with a normal response (63 +/- 11 versus 75 +/- 14 microgram/di, respectively). There was no significant correlation between an individual's serum zinc concentration and T-cell response (r = 0.16). Five patients whose T-cell responses were depressed were given intravenous zinc chloride during each dialysis run for 6 wk (10 mg intravenous zinc, three times weekly) and were evaluated before and after therapy. All five patients remained anergic to four skin tests antigens. Only one patient (who had the lowest pretreatment serum zinc concentration at 48 micrograms/dl) demonstrated significant improvement in mitogen response after zinc therapy. Although dialysis patients commonly have low serum zinc concentrations and depressed mitogen response, in our patients these two findings were generally unrelated. Additionally, supplemental zinc did not change base-line measurements of T-lymphocyte mitogen response in four of five patients studied.