Electron microscopic and light microscopic analyses were performed on Dacron® velour covered percutaneous devices implanted in the dorsum of canines for periods between 1 week and 9 months. The results indicated that although the capsular region around the implant was mature collagen after the 1st week of implantation, the tissue ingrowth region remained mostly immature collagen through 9 months of implantation. It appears that increasing the diameter of the fibres, which would decrease the chronic inflammatory response, and increasing the average distance between fibres should increase the amount of mature collagen between the velour fibres. In view of species differences between canines and humans, further investigations are needed before the relevancy of these findings can be extended to possible clinical applications with humans. © 1983.