METABOLISM OF ISONIAZID 671no breakdown products of isoniazid, such as i8onicotinic acid, were detected.Hydroly8i8 of isonicotinoylglycine. To demonstrate the production of iaonicotinic acid and glycine by hydrolysis of the metabolite thought to be isonicotinoylglycine, it was necessary to purify the urine. Urine (200 ml.) was adjusted to pH 2-5 with HCI and extracted continuously with ether for 16 hr. The residual aqueous solution was neutralized with NaOH, concentrated in vacuo and filtered from the precipitated solids. The final volume was 10 ml. One ml. of this solution was applied to paper as a thin streak and chromatographed with n-propanol:water. The band containing the i8onicotinoylglycine was cut out and eluted with three successive 20 ml. of distilled water. The combined water extracts were concentrated in vacuo to 1 ml.which was applied to paper as a streak and subjected to ionophoresis in phosphate buffer pH 6-5. The band containing the i8onicotinoylglycine was again cut out, eluted, concentrated, chromatographed and eluted as before. Part of the finalWe are indebted to Dr A. Kuper of the Brompton Hospital, London, for the supply of urine samples, to Dr E. Kodicek for a gift of nicotinoylglycine, to Dr J.Attenborough for specimens of nicotinic acid hydrazide and i8onicotinamide, and to Dr L. F. J. Parker for carrying out the ionophoretic separations.