Last year one of us1 in conjunction with Drs. Fitz, Folin and Denis compared the phenolsulphonephthalein excretion test in the urine with the non-protein nitrogen content of the blood in rabbits, in which an acute nephritis had been produced by the injection of uranium nitrate. It was found in this study that, although these two tests for renal function in a general way responded similarly in acute experimental nephritis in rabbits, there were certain variations. The excretion of the dye in the urine seemed to be a very fair indication of the rabbit's renal ability at the time of injection. On the other hand, the amount of retained non-protein nitrogen in the blood could be used as an indication of the renal efficiency at the moment only, provided the previous condition of the kidney was considered. No conclusions were drawn with regard to the prognostic value of these two