AbstractThe homopolymer of N‐(2‐hydroxypropyl)methacrylamide (HPMA) and copolymers of HPMA differing in oligopeptide side chains (‐Gly‐Gly‐OH;‐Acap‐Phe‐OH;‐Acap‐Leu‐HMDA and ‐Gly‐Phe‐Tyr‐OH) or in their content (1.0, 3.5 and 8.4 mol. % of ‐Gly‐Gly‐OH side chains)Abbreviations see appropriate Tables and Figures.were investigated with respect to their ability to induce antibody formation in inbred strains of mice. The dependence on the antigen dose on structure of the side chains and on the genetic background of the immunized organism was defined. It was demonstrated that the specificity of the antibody formed is predominantly directed against oligopeptide side chains though some part of the produced antibody is against hydroxypropyl groups. Haptens, such as arsanilic acid and fluorescein isothiocyanate, modifying the side chains, were used as drug models, and their influence on immunogenicity of HPMA copolymers was tested.The HPMA copolymers can be considered as a possible targetable drug delivery system as conditions were found under which the specific antibodies attached