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Analogues of Pyridoxine." (This lecture was illustrated by lantern slides.)Although inhibitors and poisons have been used for a long time in the study of isolated enzyme systems, it has been only in relatively recent years that physiological studies have been made with specific metabolite antagonists. Compounds with chemical structures similar to vitamins, hormones, and amino acids have been prepared which antagonize or inhibit such metabolites.' The term, antivitamin, has been applied to those compounds which counteract the function of vitamins. The inhibition ratio, or the ratio of antivitamin to vitamin that must be present for efficacy, is quite high for most antivitamins. Thus, in the case of pyrithiamine,* a thiamine antagonist, a ratio of approximately 40:l exists; that is, 40 moles of antivitamin are required to counteract the effect of 1 mole of the vitamin. Ott3 has recently reported that 2,4-dimethyl-3-hydroxy-5-hydroxymethylpyridine (desoxypyridoxine) possesses potent antipyridoxine activity in the chick. This compound has an inhibition ratio of 2:l and may therefore be considered the most potent of the vitamin B inhibitors yet discovered. Ott has also demonstrated4 that 2-methyl-3-hydroxy-4-methoxymethyl-5-hydroxymethylpyridine (methoxypyridoxine) is almost as potent an inhibitor of pyridoxine in chicks as is desoxypyridoxine. Methoxypyridoxine has been shown to possess pyridoxine activity in the rat, but no such activity has been observed with deso~ypyridoxine.~ Biochemical studies conducted by Porter, Clark, and Silbere reveal that pyridoxine-deficient rats treated with desoxypyridoxine and tryptophane excrete increased quantities of xanthurenic acid and kynurenine. Under comparable conditions, methoxypyridoxine effects a decreased excretion of these metabolic products.I n order to evaluate further the antipyridoxine activity of desoxy-This paper was presented by Doctor Mushett.