The vaginal endoscopy was performed in two Labrador Retrievers from onset of vaginal bleeding until metestrus accompanying with vaginal smear and blood progesterone concentration to investigate estral changes, and the intrauterine infusion of radiopaque fluid using vaginal endoscope (rigid 25-degree endoscope, Karl Storz) was detected by radiogrphy to determine if theis technique is feasible for future artificial insemination in the dogs. During the proestrus vaginal mucous membrane folds were edematous and a large amount of clear red discharge was present. In the beginning of estrus, the mucous membrane folds was present and the amount of the red discharge was decreased. In the estrus there were obbvious shrinkage, angulation of the membrane folds and decreasing of the discharge. In metestrus the vaginal folds started to round out and the surface appeared moist and sticky. The endoscope used for endoscopic monitoring of the vaginal mucosa was advanced until the external os of the cervix could be visualized. A plastic catheter, 8Fr guage was manupulated into the cervical os and then advanced through into the uterus. The radiopaque fluid was injected into the uterus through the catheter and radiographs taken to detect the site of insemination using the endoscopic technique revealed the exact infusion of the fluid in the uterus, consequentlyto prove that this technique is usable for more successful artificial insemintion tn the bitch.