EXCRETION of traces of porphyrins in the urine is a normal occurrence in many mammals, an outstanding exception being the American ground squirrel. Sciurus niger, which normally passes very large amounts in the urine. Adult man passes about 0.1 mg. of coproporphyrin daily in the urine and three to four times this amount of a mixture of porphyrins in the feces. In some hepatic and hematological disorders and in certain types of poisoning, particularly with lead, slight to moderate increases in urinary porphyrin occur, seldom, however, sufficient to impart a recognizably abnormal color to the urine. Almost a century ago notice was first taken of dark-red urines which did not contain blood but which showed absorption bands on spectroscopic examination similar to those of hematoporphyrin. first prepared at about that time by chemical treatment of hemoglobin and its nearer derivatives. It was noted that in some cases the condition was