The effect of four immunomodulators (BCG, Corynebacterium parvum, pyran copolymer, and levamisole) on the cellular arm of antibody-dependent cellular cytotoxicity (ADCC) was investigated in mice with 51Cr-labeled chicken erythrocytes employed as targets. All these drugs, except levamisole, stimulated the effector cells of ADCC in the spleen, but the kinetics of their effect differed. Stimulation of the effector cells of ADCC peaked on day 15 after injection of BCG and C. parvum and on day 7 after injection of pyran, which was less efficient in this respect than the two bacterial immunostimulants. The increase in ADCC activity caused by BCG and C. parvum was eliminated by treatment with carbonyl iron of the splenocyte suspensions.