The present study deals with several transitional changes occurring in the neoplastic property of an azo-dye induced ascites hepatoma of the rat since its development. With the accretion of transplant generations, the hepatoma islands showed a gradual change in general structure. There occur also transitions in transplantability and life-span of the tumor-bearing animals during the course of serial tranfers. In earlier transfer generations, the chromosome number of tumor cells of this hepatoma fluctuated within a very wide range, without showing any distinct modal values. With the increase of transfer generations, the chromosome number showed a rather narrow range of variation with the occurrence of distinct modal values at 69-71.<br>It can be can be concluded on the basis of the present findings that the constancy of the stem-line, while it is very pronounced, is not necessarily fully stable, and that under certain conditions the tumors have undergone numerical and structural changes in their stemline-chromosomes during serial transfers. Apparently such chromosomal changes will cause the transition of the genotype of the tumor which will in turn produce the shifts in the property of the tumor.