An immune response (Ir) gene(s) controlling responses to synthetic GA in mice is well documented. This specific Ir gene is linked to the major histocompatibility complex of the species. Mice of the H-2a,b,d,f,k,r and s haplotypes produce high titer antibodies and thus are high responders; mice of the H-2 haplotypes j, ja, p and q produce no detectable antibody and are nonresponders. The response is all or none and high response is dominant. Attempts to detect an Ir-GT gene after immunization with 2 GT random copolymers were unsuccessful. GT antibody could be produced after immunization with GT-methylated bovine serum albumin aggregates.