From the results described above, it is clear that the level of EP, most of which is protoporphyrin, rises in the blood of tumor bearing animals. Protoporphyrin combines with iron, and changes to protoheme, which is the prosthetic group of hemoglobin and catalase. Although, in the case of tumor bearing animals, the possibility of supressed synthesis of protein moiety of hemoglobin cannot be neglected, accumulation of protoporphyrin observed here may be considered as an evidence of the iron metabolism disturbance. It is known that in iron deficient anemia, EP level is very high when compared with that in the pernicious anemia (8). Furthermore, it was reported that lead poisoning affected the mechanism of the iron incorporation into protoporphyrin, and increased the FP (9). Recently, Schwartz et al. reported of the presence of erythrocytic and hepatic types in porphyria (10). Also in the tumor bearing animals, high level of protoporphyrin in liver was recognized in onr laboratory.