Segments of open Dacron mesh grafts were subcutaneously implanted in rats and harvested for a period of up to 12 weeks after operation at serial intervals. The gross and histologic events of the host response to the external surface were compared to that of segments of low-porosity Dacron velour implanted in a similar fashion. Mature collagen, generously vascularized with new capillaries, was noted throughout the mesh within three to four weeks, while a tightly bonded inner fibrous layer had formed from the surrounding tissues. Major segments of velour floated in amorphous caseous material for up to five weeks. These pools of debris with their concomitant inflammatory response slowly resolved during a ten-week period. This prolonged healing may contribute to eventual graft closure by progressive fibrosis and extrinsic contracture.