Glyoxylic acid reacted with o-aminobenzaldehyde and glycine to yield a yellow product, whose absorption maximum was at 440mμ. Glycine could be replaced by ω-amino acids, e. g., γ-aminobutyrate, and aliphatic amines, but not by α-amino acids. The effects of pH, kind and concentration of buffers, concentration of o-aminobenzaldehyde, and incubation time on the reaction were investigated to establish the optimum conditions. Microamounts of glyoxylate (0.05_??_1.5μmoles) were determined rapidly by this simple method with satisfactory results. α-Keto acids such as α-ketoglutarate reacted far less effectively; almost no appreciable interference with quantitative estimation of glyoxylate occurred with them. This procedure is applicable for the assay of enzymes which catalyze the formation of glyoxylate, e. g., isocitrate lyase and glycollate oxidase.