The authors demonstrate the transmissibility of the tumour of Yoshida by means of definitely acellular, tumoural extracts. Neoplasia occurred in 11 out of 12 new-born mice i.p. inoculated as above. It is noteworthy that the neoplasia developed not only ascitic but also solid (nodes and tumoural nodules) prevalently at pulmonar level. Derived tumoural ascites are transmissible to the adult rat.