Activity of acid phosphatase was determined in rabbit kidneys under subcapsular implantation of polyester-based polyurethane films (A-10) and films (D-1) containing the links of L-phenylalanyl-L-serine dipeptide in the main chain of the polymer. Optimal conditions are chosen for detecting activity of this enzyme in homogenates and in the lysosome enriched fraction of rabbit kidneys with L-glycerophosphate used as a substrate. Activity of acid phosphatase under the A-10 specimen implantation increases on the 7th and 14th day and later (during a year) does not differ from the normal level. Under the D-1 spectrum implantation the acid phosphatase activity remains increased for a longer period--up to one month. It is possibly due to the fact, that this polymer contains dipeptide fragments and is subjected to a more intensive enzymic destruction than the A-10 specimen.