Cathepsin D activity was compared during the healing period of polyester DALLON-standard and DALLON-double velour prostheses implanted into the abdominal aorta of dogs. During first months following the implantation cathepsin D activity is considerably higher in all the layers of both types of prostheses than in the aorta. The normalization of this enzyme activity occurs significantly faster during the healing of DALLON-double velour prostheses than in that of DALLON-standard. This fact shows greater progress in the protein metabolism normalization during the process of healing and tissue reconstruction in DALLON-double velour prostheses.