Technical Abstract: Recommendations for vitamin A intake are based on maintaining liver stores of equal to or greater than 0.070 umol/g, which is sufficient to maintain normal vision. We propose that higher levels may be required to maintain normal immune function. To test this hypothesis, we conducted an 8 wk residential study among 36 healthy Bangladeshi men with low vitamin A stores. Subjects were randomized to receive vitamin A (240 mg in 4 doses) or placebo during study wks 2 and 3. Vitamin A stores were estimated by isotopic dilution at wk 8. Total T-cells, the ratio of naïve-to-memory T-cells and mitogen-induced lymphocyte proliferation were positively and significantly correlated with vitamin A stores (P<0.05). Mitogen-stimulated IL-2, IL-4 and TNF' increased significantly (P<0.05) in the vitamin A but not placebo group after supplementation while IL-10 production was significantly and negatively correlated with vitamin A stores (P<0.05). Segmented linear regression analysis revealed that naïve T-cell counts and T-cell blastogenesis were positively associated with vitamin A stores and memory T-cell counts were negatively associated with stores above but not below 0.070 umol/g liver. These data show that increasing vitamin A stores above the level that maintains normal vision enhances some measures of T cell-mediated immunity, suggesting a difference in requirements for maintaining vision and immune function.