THE metabolites appearing in the urine after an oral load of L-tryptophan have been separated by paper, thin-layer and column chromatography. After ingestion of L-tryptophan (70 mg/kg body-wt.) the urine was collected at timed intervals over the next 24 h. Aliquots of the urine were examined by two-way paper chromatography (n-butanol–acetic acid–water, 12 : 3 : 5, followed by 20 per cent KCl in water), and by thin-layer chromatography on silica gel using chloroform, methanol, acetic acid (76 : 22 : 2 by volume). The metabolites were located with Ehrlich and Pauly reagents1 and by fluorescence in ultra-violet light at two wave-lengths (253 and 366 mµ).