A determination method of urinary vanilpyruvic acid was developed by high-speed liquid chromatography. Sample urine was acidified and extracted with ethyl acetate. After evaporation of the organic solvent, the residue was left over phosphorous pentoxide to complete the conversion of keto form to enol form and dissolved in methanol. The methanol solution was injected into a high-speed liquid chromatograph equipped with a column of Hitachi Gel No. 3010 (spherical porous particles of styrene-divinylbenzene copolymer) and a ultraviolet (UV) monitor (280 nm). Vanilpyruvic acid was eluted with a mixture of 0.05 M tartrate buffer and methanol (85 : 15, v/v) varying the pH of the buffer from 3.15 to 5.25. The quantity of vanilpyruvic acid was determined from the peak height. By the present method, vanilpyruvic acid was found in urine of patients with neuroblastoma, a Parkinsonian patient treated with L-3, 4-dihydroxyphenylalanine. However, this acid was not found in urines of normal subjects.