Since Borrel (1906) pointed out the relationship between Cysticercus fasciolaris and sarcoma of the rat liver (1), several investigators have reported one or more cases of Cysticercus sarcoma. In July 1920, the first experimentally produced Cysticercus sarcoma was observed by Bullock and Curtis (2). This and 67 others were observed in rats purchased from several breeders, each of whom had for some time supplied the laboratory with rats from his own colony. Pregnant females from each of these stocks were isolated, and their progeny formed the “foundation stock” with which a pedigreed colony was started. At the beginning of the present analysis (June 1932) 52,223 animals from completed matings had been autopsied. Of these, 26,172 were infested with the parasite, 13,120 survived infestation for at least eight months (the minimum period of infestation observed in the case of a bearer of a Cysticercus sarcoma), and 3,285 had Cysticercus sarcoma. Besides these, 316 unpedigreed descendants of the purchased animals had the malignant complication of the Cysticercus disease. The authors (3) have recently published a brief statement of some of the major facts shown by this investigation.