The decarboxylating activity of l([long dash])-tyrosine, d,l-tyrosine, d,l-alanine, d,l-serine, l( + )-arginine-HCl, proline, quinine and aneurin (vit. B1) was detd. by measuring the amt. of CO2 formed when the sub-stances were heated with pyruvic acid. Amts. of the substances varying between 1.6 and 28.8 mg. were added to 0.2 cc. of pyruvic acid. After 2 hrs.'' heating, from 10 to 12 mg. of the amino acids gave yields of CO2 varying between 20 and 67 mg. Quinine was as active, but aneurin was less active than the amino acids. The reaction was retarded by 0.02 cc. of H2O, but was accelerated by 0.05 cc. of pyridine and nicotine. Acetoin, CH3-CO-CHOH-CH3, was formed during the decarboxjdation of pyruvic acid in the presence of d,l- and l( + )alanine, d,l-phenylaminoacetic acid, 1([long dash])-and d,l-asparagine and asparaginic acids. For identification purposes, acetoin was prepared by the decarboxylation of pyruvic acid in the presence of levorotatory phenylamino-acetic acid or 1([long dash])-asparagine. The acetoin thus prepared was optically inactive and was isolated as the semicarbazone, m. 192[degree].