In order to study the possibility of porphyrin to become bile pigment precursors, the relations between free porphyrin in erythrocytes, especially protoporphyrin, and intracorpuscular bile pigment precursors were experimentally observed. The results were as follows: 1. A part of protoporphyrin which increased was observed to change quickly into bile pigment precursors in the erythrocytes of a phlebotomized anemic or phenylhydrazine HC1 administered rabbits where reticulocytosis occurred. 2. This transformation of protoporphyrin into bile pigment precursors were also observed in preserving canine erythrocytes where reticulocytosis was caused by phlebotomies. 3. Judging from the variations of intracorpuscular easily split off blood iron, it seemed appropriate to consider that this transformation occurred after the formation of hems or hemoglobin. In the above experiment, however, of preserving erythrocytes of a phlebotomized anemic dog, the plainly direct transformation of protoporphyrin into bile pigment precursors were also observed. 4. In preserving canine erythrocytes with or without the addition of ascorbic acid, the increase of protoporphyrin and of bile pigment precursors were also observed. However, it is difficult to account for the relations betwaen these two; the increase of bile pigment precursors may be ascribable to the breakdown of hemoglobin.
5. Intracorpuscular free coproporphyrin was obsarvei to increase in those erythrocytes after phlebotomies. phenylhydrazine HC1 aiministratioa, or preservation with the addition of ascorbic acid. This increase may more properly be ascribed to protoporphyrin in the formation process of hemoglobin than to bile pigment precursors. On the other hand, free uroporphyrin in erythrocytes did not show any significant variations. 6. Protoporphyrin mixed with chloroform extract did not hinder the microquantitative analysis of bile pigment precursors by fluorescence.