Various kinds of epithelial and non‐epithelial tumors, and tumor‐like lesions spontaeously developed in long‐lived mice of strains A/St, C57BL/6 and CBA, and of (C57BL/6 x CBA) F1, hybrids, all of which had been fed in the 2nd Department of Pathology, Gifu University School of Medicine.Some tumors were successfully transplanted into the same strain of mice. An interesting tumor line showing phagocytic activity and growing only in the liver even when inoculated subcutaneously, which was obtained from a reticulum cell neoplasm, Type A by Dunn, originated in the liver of a (C57BL/6 X CBA) F1hybrid male