THE aim of this work was to obtain auxin a, first isolated by Kögl, Haagen-Smit and Erxleben1 from human urine in 1933. In their isolation procedure, these workers extracted a urine concentrate at an acid pH with ether. The ether extract in turn was partitioned into a neutral and an acid fraction with sodium bicarbonate. The auxin was present in the acid fraction and was subjected, in the final stages of the isolation procedure, to refluxing with methanol containing 1.5 per cent hydrochloric acid. This step was followed by high-vacuum distillation, yielding a crystalline material with high auxin activity which they called auxin a.