In the present studies we have confirmed that the random copolymer of L-glutamic acid50-L-tyrosine50 (GT) fails to induce an antibody response in a large number of inbred strains of mice. Nevertheless, GT complexed to methylated bovine serum albumin (MBSA) elicits a GT-specific IgG PFC response in vivo. Furthermore, injection of BALB/c mice with 10 to 100 mug of GT specifically decreases their ability to develop anti-GT PFC responses to a subsequent challenge with GT-MBSA. GT-specific tolerance can be transferred to normal, syngeneic recipients by spleen cells or thymocytes of GT-primed animals. These results indicate that the stimulation of suppressor cells can be observed in nonresponder mice with another synthetic polypeptide besides GAT. Various parameters of GT-specific immunosuppression in BALB/c mice are described. The application of these techniques to the study of the genetic factors controlling the stimulation of specific immune suppression is discussed.