1. Etiohemoglobin and dimethylprotohemoglobin were prepared from corresponding hemes and apohemoglobin. These two artificial hemoglobins showed higher affinity for oxygen and ethylisocyanide (EIC) than natural hemoglobin. The “n” value in Hill's equation was calculated as 1.3 from EIC dissociation curves, indicating decreased heme-heme interaction. 2. The half-denaturation temperature of etiohemoglobin and dimethylprotohemoglobin as well as of apohemoglobin was 41°, in contrast to 61° in protohemoglobin, reconstituted protohemoglobin and protoporphyrin-globin. 3. Sedimentation constants of etiohemoglobin and dimethylprotohemoglobin were the same as that of apohemoglobin. 4. The rotatory dispersions of etiohemoglobin and dimethylprotohemoglobin indicated that the helical contents of these proteins were lower than that of protohemoglobin.