Abstract
The excretion of an excess of vit. B6 was demonstrated in patients receiving isoniazid (INH), with the irregular appearance of abnormal amts. of xanthurenic acid following a test dose of tryptophane. The effect is more marked in those getting a higher dose of INH. Such laboratory evidence of B6 abnormality provides a cause of peripheral neuritis. Preliminary results suggest that the addition of pyridoxine to a high dose of INH prevents neuritis, which otherwise occurs in 40% of the cases.