The endoscopic injection of collagen paste has become popular to treat urethral sphincter mechanism incompetence (USMI). To assess the biocompatibility of homologous dog and xenogenic avian collagen, we injected each material into the urethral wall of six female dogs and examined the host tissue response histologically over a period of 12 weeks. We also compared the urethral pressure profile before and weekly after the implantation. Antibody titers in the sera of the dogs, which received the xenogenic avian collagen were measured, as the avian collagen has differences in its protein sequences in comparison to dog collagen, which may enhance its immunogenicity. The homologous dog collagen was also used in one dog, which suffered from USMI and did not respond to conservative treatment or colposuspension. Both types of collagen implants were readily found in all the urethrae and their appearances did not change over a period of twelve weeks. The homologous dog collagen was also found to be present 12 months after implantation in the clinical case, which maintained to be continent. The inflammatory reaction was similar with both types of collagen, however the presence of inflammatory cells was slightly increased in association with the use of homologous dog collagen. Although we observed in most dogs a trend towards an increased maximal urethral closure pressure after collagen implantation, the variability of the results even in each dog suggests that the use of urethral pressure profilometry is limited in assessing the clinical effect of the collagen implants. The use of xenogenic avian collagen did not lead to a major increase in the antibody titer in the sera of the dogs.