A vitamin B-6 (B-6) intake higher than the current Recommended Dietary Allowance (RDA) has been found to provide an improvement in immune system. Seven premenopausal women consumed their usual diet with the exception of foods relatively high in vitamin B-6 for a total of 27 d. After 7 d, all subjects received a multivitamin supplement containing 2mg B-6 and 4 subjects were given an additional 50mg of B-6 supplement for 20 d. Lymphocyte response to phytohemagglutinin (PHA) was measured before and after the supplementation. To determine the effect of different forms of B-6 on lymphocyte proliferation, cell culture media supplemented with pyridoxal (PL) and PLP, as well as B-6 free media, were tested. A 50mg B-6 supplement significantly increased vitamin B-6 status. There was no further enhancement on lymphocyte proliferation when subjects were taking an additional 50mg of vitamin B-6 supplement. In general, lymphocyte proliferation in media with either PLP or PL did not show any prominent difference. These [m-dings suggest that there may be no further benefits of a B-6 dose beyond twice that of the current RDA on lymphocyte proliferation. Further studies are necessary to examine the effect of the B-6 intake level on activities of enzymes involved in cellular B-6 metabolism in lymphocytes to provide substantial insight into the mechanisms underlying the role of B-6 in the lymphocyte proliferation.