F344 male rats were given 90 ppm diethylnitrosamine in their drinking water ad libitum in two cycles. Livers containing neoplastic nodules, hepatomas, and no sarcomas in the sections sampled were digested in parallel with 0.05% collagenase, 0.1% Pronase, or 0.25% trypsin. Cells were transplanted into 9- to 19-day-old F344 rats. Despite the absence of sarcomas in the sections examined microscopically from each such liver before digestion and the presence of multiple hepatomas in all sections examined, vascular sarcomas, probably angiosarcomas, were observed in a large proportion of animals injected with the suspensions of cells; hepatomas were not observed in these animals. Morphology by light microscopy, immunohistochemical demonstration of factor VIII, histochemical demonstration of alkaline phosphatase, and the presence of Weibel-Palade bodies strongly suggest that these tumors are angiosarcomas. Similar tumors developed from cells obtained in parallel with the aid of Pronase, collagenase, or trypsin. Cell suspensions obtained with Pronase yielded tumors with the shortest latent period between the injection of cells and the death of one-half of the transplant recipients. The procedure that we used provides a consistent method for the production of transplantable sarcomas. The absence of sarcomas in the single sections taken from donor livers and multiple sections of similar livers not used for transplantation suggests that transplantability of these sarcoma cells is acquired very early in this neoplasm.