By means of histological method and the scanning and transmission electron microscope healing processes of two types of Polish prostheses: DALLON-standard and DALLON-double velour were compared. The experiments were carried out on 36 dogs. The two types of prostheses mentioned were implanted in abdominal aorta. The grafts were removed 1, 4 and 12 months after implantation. The performed studies showed that although the sequence and nature of morphological changes leading to the reconstruction of the vascular wall in both types of grafts were similar, the development of the neointima as well as the formation of the neo-adventitia firmly accreted with surrounding tissues were considerably faster in double velour DALLON prostheses. Unlike in standard DALLON prostheses, the neointima of double velour DALLON grafts was rich in cells, had elastic fibres. Already after 12 months double velour DALLON grafts were completely covered by endothelial cells, which proves better reconstruction of the vascular wall. Rapid endothelial cells coverage of the lumen surface prevents thrombosis. Morphological differences observed in endothelial cells covering the neointima of standard grafts and double velour graft suggest the existance of various sources of endothelialization in both types of grafts.