A number of nonamino organic acids associated with inborn errors of metabolism can be detected by gas chromatography. The organic acids are extracted into ethyl acetate and diethyl ether, the extracts combined, and the solvents evaporated under nitrogen. The residue is taken up in carbon disulfide and an aliquot chromatographed on 5% neopentyl glycol adipate to separate short-chain fatty acids (C 2 to 6). The remaining carbon disulfide is evaporated, the residue taken up in methanol, and the acids are methylated with diazomethane. The solvent is evaporated, the residue taken up in tetrahydrofuran, and an aliquot chromatographed on 15% diethylene glycol succinate to separate keto, hydroxy, and dicarboxylic acids. Chromatographic patterns for normal and abnormal urines have been established. Four cases of congenital methylmalonic aciduria have been diagnosed by this procedure.