Rats with Walker tumor injected intramuscularly in both hind legs and subjected to forced swimming for 15 min daily for 10 days displayed a trend toward decreased lesion size, especially in older intact animals as compared to unexercised intact or bilaterally adrenalectomized controls. Secondary tumor nodules occurred at the lower abdominal or inguinal areas and appeared to be more extensive in the older exercised rats. The survival rates of forced exercised rats bearing Walker tumor cortically did not differ significantly from the respective controls as was also the case with adult BDF1 mice withintraperitoneal or cortical l1210 tumor and subjected daily to electroshock at 0.25mA for 15 min.