In the course of experiments performed on rats to produce hypertension by wrapping cellophane film around one kidney, Oppenheimer1 and his associates of Columbia University noted that sarcomas developed in several rats in the neighborhood of the cellophane. The sarcomagenic properties of cellophane film were therefore tested on 110 adult male rats. In 55 of these the left kidney was loosely wrapped with "highstretch" cellulose sausage casing, according to the method introduced by Page.2 In the other 55 rats, a piece of cellophane 1 inch (2.5 cm.) square was embedded subcutaneously in the abdominal wall and kept in place by a surgical suture at each corner. Among the rats with the wrapped kidney, 23 survived over eleven months. Of these, 8, or 34.8 per cent, had large well defined tumors. Of the 55 rats in which the cellophane was embedded subcutaneously, 42 survived beyond eleven months.