Recommendations for vitamin A intake are based on maintaining liver stores of≥ 0·070 μmol/g, which is sufficient tomaintain normal vision. We propose that higher levels may be required to maintain normalimmune function. To test this hypothesis, we conducted an 8-week residential study amongthirty-six healthy Bangladeshi men with low vitamin A stores. Subjects were randomised toreceive vitamin A (240 mg in four doses) or placebo during study weeks 2 and 3.Vitamin A stores were estimated by isotopic dilution at week 8. Total T-cells, the naiveT-cells:memory T-cells ratio and mitogen-induced lymphocyte proliferation were positivelyand significantly correlated with vitamin A stores(P < 0·05). Mitogen-stimulated IL-2,IL-4 and TNFα increased significantly(P < 0·05) in the vitamin A but notplacebo group after supplementation, while IL-10 production was significantly andnegatively correlated with vitamin A stores(P < 0·05). Segmented linear regressionanalysis revealed that naive T-cell counts and T-cell blastogenesis were positivelyassociated with vitamin A stores above but not below0·070 μmol/g liver. These data show that increasing vitamin Astores above the level that maintains normal vision enhances some measures ofT-cell-mediated immunity, suggesting a difference in requirements for maintaining visionand immune function.