Aging is associated with a progressive decline in the immune system and a greater susceptibility to infection. This double-blind, placebo-controlled study, examined the effect of a vitamin and trace element supplement on immune responses of healthy, noninstitutionalized elderly subjects. Forty-seven subjects aged 61-79 years were randomly assigned to receive placebo or micronutrient supplementation for one year. Thirty-five individuals completed the one-year study. Immune function was assessed before and after the period of supplementation. Cell-mediated immune function assessed by the number of T cells and subsets remained constant in the supplemented group and there was a significant increase in CD57 natural killer cells. In contrast, a significant decrease in T cells, CD4 cells, and CD4: CD8 ratio was noted in the placebo group. Supplementation with micronutrients can play a crucial role in the maintenance of normal immune function in the elderly.