Reduction of the carbonyl group in tetrahydrodemethoxycolchicine to methylene was effected by preparing the dimethylmercaptol which on heating with Raney nickel gave hexahydrodemethoxydesoxycolchicine. Phosphorus pentoxide in refluxing xylene degraded hexahydrodemethoxydesoxycolchicine to the desacetamido compound which was directly hydrogenated to octahydrodemethoxydesoxydesacetamidocolchicine. The ultraviolet and infrared absorption spectra of the various degradation products were determined and found to be compatible with the assigned structures. By the application of purification procedures to desiccated liver powder, concentrates of the citrovorum factor (I) with substantially the same activity, weight for weight, for Leuconostoc citrovorum 8081 as the compound resulting from the formylation and reduction of pteroylglutamic acid (II) were obtained. Differences in the microbiological activity of the respective acid degradation products and the absorption spectra lead to the belief that the synthetic compound is not the citrovorum factor as obtained from liver. Of three mutant strains of Escherichia coli responding to histidine, one (26-25) excretes a substance (identified as L-histidinol) that satisfies the histidine requirement of the other two (26-24, 26-24D1), suggesting L-histidinol is an intermediate in the biosynthesis of histidine in E. coli. Carp thiaminase, which destroys thiamine by cleaving off the thiazole moiety, was found to catalyze the synthesis of pteroic acid and pteroylglutamic acid from 2-amino-4-hydroxy-6-pteridylmethyl-(4'-methyl-3'-hydroxyethylthiazolium) bromide and amines (p-aminobenzoic acid or p-aminobenzoylglutamic acid), with significantly higher yields than without the enzyme. Lactobacillus bulgaricus 09 has been found to require either orotic acid or ureidosuccinic acid as an essential growth factor, and experiments were conducted to investigate the role of these compounds in the biogenesis of the pyrimidine components of ribonucleic acid.