A BIOCOMPATIBLE HYDROGEL, is provided for use in the treatment of humans for cosmetic and functional defects (e.g. in mammas, vocal cords, penis, etc. as endoprostheses), in the provision of intratissue storage sites the prolonged-action medicinal preparations, in various applications as electroconductive immersion media, and in the life-long tamponing of caverns. It contains an acrylamide-based polymer produced in the presence of an initiator of radical polymerization in apyrogenic water as the dispersion medium. An increase in elasticity, shape retention capability, and stability of bulky implants, as well as corresponding therapeutic and cosmetic efficacy, mainly in the endoprosthetic applications is achieved due to the hydrogel containing cross-linked polyacrylamide produced by using a biocompatible cross-linking agent, such as methylene-bis-acrylamide, and preferably a mixture of ammonium persulfate and tetramethylethylenediamine as the initiator of polymerzation. A preferred concentration of the novel polymer in the hydrogel is from 3.5 to 9% by mass.