In two studies we tested the effect of vitamin B-6 (B-6) intake on in vitro lymphocyte, proliferation and IL-2 production in healthy young women. In Study I, 6 women were fed a constant diet containing 0.84 mg (4.96 μmols) of B-6 for 12 d, and 1.24 mg (7.33 μmols) and 2.44 mg (14.42 μmols) of B-6 during two subsequent 10-d periods. Lymphocyte proliferation in response to the mitogens concanavalin A (Con A) and pokeweed mitogen (PWM) was significantly higher (p < 0.05) at 2.44 mg than at 0.84 mg intake and the pre-study value. In Study II, 10 women who consumed their self-selected diets were randomly divided into a PN and a placebo group of five each. Following a 5-d baseline period, the PN group received a daily supplement of 1.5 mg (7.29 μmols) and 50 mg (243 μmols) pyridoxine.HC1 (PN.HC1) for 7 and 6 d, respectively. This was followed by a 28-d washout period during which no supplement or placebo was administered. After daily 1.5 mg supplementary PN.HC1 for seven days, lymphocyte proliferation in response to phytohemagglutinin (PHA), Con A and PWM, and IL-2 production were significantly higher than the baseline (p < 0.05) and that of the placebo group (p < 0.05). The 50 mg PN.HC1 supplement increased IL-2 production, but not lymphocyte proliferation as compared with the 1.5 mg PN.HC1 supplement period. Lymphocyte proliferation and IL-2 production were significantly correlated with lymphocyte pyridoxal 5'- phosphate concentrations (p < 0.01). We conclude that a B-6 intake of 1.5 to 2 times the RDA improves lymphocyte proliferation and IL-2 production in healthy young women and this effect of B-6 on immunocompetence is transitory. To explore the basis for the effect of B-6 on immune function, putrescine was added to the culture medium (2 - 200 μmol/L). In vitro lymphocyte proliferation and IL-2 production were not changed by the addition of putrescine under our experimental conditions. / Graduation date: 1995