We investigated the effects of iron deficiency anemia, iron repletion, and iron chelation by deferoxamine on protein kinase C (PKC) activity, an enzyme that plays a crucial role on T lymphocyte proliferation. The study involved 23 control (C), 18 pairfed (PF), and 24 iron deficient (ID) mice or ID mice that were repleted for 3 (n = 14), 7 (n = 17), or 14 (n = 14) days. The low iron (0.09 mmol iron/kg) and iron-supplemented (0.9 mmol iron/kg) diets were fed to mice for 53 days. Mean hemoglobin, hematocrit, and liver iron stores of ID mice were one third of those of C mice. Lymphocyte proliferation was reduced (P< 0.05) in spleen and purified T cells in ID but not PF mice. In concanavalin A, phytohemagglutinin, and anti-CD3 antibody- treated and untreated cells that were incubated in serum-free and serum- containing medium, PKC activity was significantly (P < 0.05) reduced in ID but not PF mice and returned to normal before correction of anemia. In mitogen-treated cells, while the ratios of membrane-bound to cytosol activity increased nearly seven-fold (from 0.4-0.63 in resting cells to 1.43-7.23) in spleen cells from C, PF, and repleted mice and 11-fold in T cells (P < 0.005), they remained below 1 in ID mice suggesting reduced translocation. In vitro iron chelation by deferoxamine for 120 min prior to cell activation reduced (P < 0.05) PKC activity by 46-60% in C and PF and 28-53% in ID mice. The data suggest that: 1) it is iron-deficiency but not anemia or differences in the proportion of immunocompetent T cells that reduced PKC activity in cells from ID mice; 2) reduced PKC translocation may play an important role on altered lymphocyte proliferation and associated functions in iron- deficient individuals.