The Yoshida ascites sarcoma is one of the well-kown and long-lasting transplantable tumors of the rat and has furnished a favorite material for experimental studies in the field of cancer research since its establishment in 1943 by T. Yoshida. Recently, it has been reported that this tumor shows a derivation into serveral sublines which differ in the chromosome pattern with a change in the tumor type. Makino and Sasaki (1958) have established the occurrence of four chromosomal sublines, referred to as A, B, C and D, that were derived from the Yoshida stock tumor. It may not be uncalled for to make a comparative survey of the transplantability of these four sublines in order to provide a back-ground for various fields of cancer research.<br>Four sublines of the Yoshida sarcoma have been maintained in Makino's laboratory during over 100 serial transfer-generations using rats of the following seven strains, Wistar (W/Ma), Wistar (wp), Wistar Pacific, Wistar King-A, Gifu, Tokyo and Castle's Black×Wistar King-A. The data presented in this paper were based on the above transplantation records. In addition, the following four strains of rats, Long-Evans, Buffalo, Fischer and Albany, were used for the examination of the susceptibility of the Yoshida sublines, but not for the serial transfer of the tumors.<br>The transplantation rate and survival days of tumor-rats were observed in four sublines of the Yoshida sarcoma with various strains of rats. The results are presented in Table 1. For the rats of the following eight strains, Wistar (W/Ma), Wistar (wp), Wistar Pacific, Wistar King-A, Gifu, Tokyo, Castle's Black×Wistar King-A and Long-Evans, the four tumor sublines under study gave a similar transplantability showing 70 to 100 per cent lethal takes. For the rats of Buffalo, Fischer and Albany strains, however, the transplantability of the four sublines was different in more or less degree. Noteworthy is the fact that subline C was wholly nonsusceptible to rats of Fischer strain, while subline D showed a high transplantability at 80 per cent to rats of the same strain. A similar situation seems to occur in rats of Baffalo strain: the transplantability in them was 33 per cent for subline C and 75 per cent for subline D. It is interesting to note that subline D was derived from subline C through the inoculation of their tumor cells subjected to freezing (cf. Makino & Sasaki 1958, Sasaki 1958). In rats of Wistar (W/Ma), Gifu, and Tokyo strains, the four sublines showed a considerably high transplantability giving 90 to 100 per cent lethal takes; especially in the W/Ma strain over 97 per cent of animals died of the tumor.<br>It is rather interesting to know that the transplantation rate and survival days of tumor-rats somewhat differ by the strain of rats used for translpantation. For instance, the transplantability of the Yoshida sarcoma in Wistar rats, which contain several substrains, differs according to the rats of different substrains. Such differences may be caused on the one hand by the difference of the tumor line or subline, and on the other hand by the difference of the strain of rats employed. A similar situation seems to exist in the life span of tumor-bearing animals: the life span differs either by the rat strains or by the tumor sublines (table 1 and 2).