The male and female mice were irradiatrd with different doses (from 0 to 200 cGy) of ,60,Co gamma ray, their splenic antibody forming cells were measured with the Plaque Forming Cell (PFC) technique. The results show that the PFCs of both the male and female mice were depressed and the depression was of dose-depending. When the dose was 200 cGy, about 85% of the PFCs were inhabited. No differece in the radiosensitivity between the male and female mice was found.