Toxaphene was fed to female weanling Swiss-Webster mice at dosages of 10, 100, and 200 ppm for 8 wk. Immunologic assays revealed depressed IgG antibody formation in those animals receiving 100 and 200 ppm toxaphene, as compared to controls. Cell-mediated immune responses were not affected in the toxaphene-exposed mice. In another experiment, mature female mice fed the same amounts of toxaphene were mated 3 wk after feeding began and were maintained on the diets until 3 wk after parturition, at which time the pups were weaned onto the control ration. Assays performed on the offspring 8 wk after their birth revealed suppressed antibody formation in the 100-ppm-toxaphene group and enhanced antibody formation in the 200-ppm group. The cell-mediated immune response was suppressed in the offspring from the 100-ppm group, while no change from the controls occurred in the other groups. Phagocytic ability of macrophages was significantly reduced in all toxaphene-treated groups, but to a greater extent in the offspring of the mice that consumed 100 ppm toxaphene.