Abstract 1. 1. The “single” type mouse hemoglobin has one major, three minor, and one nonheme component. Strain C57 appears to be exceptional (zone M Ic is missing) but there is some existing evidence that the minor component M Ib may be further resolved. 2. 2. Two types of “diffuse” hemoglobins were found. Strains C3H and C3HB contain two major, three minor, and one nonheme component; AKR and A contain three major, two minor, and one nonheme component. 3. 3. While the “single” type mouse hemoglobins seem to be characterized by one large major component, very real differences exist in the over-all composition of all the hemoglobins studied, both in the major and minor components. 4. 4. It is proposed that a modification of the nomenclature of Allen et al. (3) for the components of human hemoglobin be developed for other species.