The effect of cooked wheat bran on the bioavailability of vitamin B-6 (B-6) was determined in 10 men, aged 20 to 35 years. The subjects consumed a constant diet with and without the addition of 15 g wheat bran during three successive 18-day periods in a switch-back design. Half of the subjects received the additional bran during periods 1 and 3; the other half consumed the bran during period 2. The bran and nonbran diets supplied, respectively, 1.69 and 1.66 mg of B-6 daily. Plasma total B-6 and pyridoxal phosphate (PLP), urinary 4-pyridoxic acid (4-PA), and urinary and fecal B-6 were determined at regular intervals during each period. Bran significantly increased fecal B-6 (P less than 0.05) and decreased urinary 4-PA (P less than 0.01). Bran also significantly depressed plasma B-6 (P less than 0.01) and PLP (P less than 0.05). These results indicate that the addition of 15 g of wheat bran to the diet decreased the bioavailability of B-6. Since this decrease was modest, never exceeding 17% (based on urinary 4PA and B-6), this amount of bran will not adversely affect B-6 status when intake of the vitamin is adequate.