Thirty elderly long-stay patients were randomly allocated to receive either placebo or dietary supplementation with vitamins A, C and E for 28 days. Nutritional status and cell-mediated immune function were assessed before and after the period of supplementation. Following vitamin supplementation, cell-mediated immune function improved as indicated by a significant increase in the absolute number of T cells (p less than 0.05), T4 subsets (p less than 0.05), T4 to T8 ratio (p less than 0.01) and the proliferation of lymphocytes in response to phytohaemagglutinin (p less than 0.01). In contrast, no significant changes were noted in the immune function of the placebo group. We conclude that supplementation with the dietary antioxidants vitamins A, C and E can improve aspects of cell-mediated immune function in elderly long-stay patients.