The conjugate of bovine serum albumin (BSA) with polyacrylic acid, in contrast to pure BSA and the mixture of BSA with polymer, induces a pronounced primary humoral response. The injection of the conjugate in Freund's complete adjuvant leads to considerable immune response to BSA, 30-40 and 100-130 times more intensive than that produced, respectively, by the injection of the conjugate alone or BSA in the adjuvant.