Abstract
A strain of T. equinum requires nicotinic acid for growth. This may be replaced by an equal amt. of nicotinamide or by a comparatively large amt. of L-tryptophan. After growth of the fungus in a tryptophan medium the presence of nicotinic acid was detd. by biological assay with Lactobacillus casei. This provides evidence that tryptophan is a precursor in the formation of nicotinic acid by T. equinum. The relationship of T. equinum to T. faviforme is discussed.