AbstractExperiments were investigated on animals' biological tolerance of the copolymers ofN‐substituted methacrylamides with the monomers which can be considered for uses in the modification of the monomeric backbone. The group ofN‐substituted methacrylamides is the second one in the series of hydrophilic polymers arranged according to their increasing resistance to hydrolysis, and it follows immediately after the esters of methacrylic acid. Histological analysis has shown that the copolymer ofN‐ethyl methacrylamide with methyl methacrylate is the best tolerated polymer of this group. In the case of copolymers with butyl acrylate and butyl methacrylate, in the first days after implantation a stronger and more cellular capsula was formed, and an inflammation was observed in the surroundings of the encapsulated implant. Starting from day 30, however, no differences are found in the encapsulation, and the result of healingin of all the polymers is always favorable. No cancerogenic effects were observed; calcification was found only sporadically in the case of the copolymer with butyl methacr