The purpose of the present study was to evaluate the therapeutic effect of intrauterine chitin suspension on endometritis in cows. In experiment 1, 50 ml chitin suspension (60 and 80 mg/ml in saline), definitely induced estrus. Therefore, 50 ml of the 60 mg/ml suspension was injected into the uteri of Japanese Black cows (3-5 years old, average weight 530 kg) with a normal estrus cycle or endometritis in further experiments. In experiment 2, 21 parous Japanese Black cows with a normal estrus cycle received chitin on day 8-12 of estrus (the day on which estrus occurred was designated day 0). Nineteen of the 21 (90.5%) came into estrus 5-8 days after administration, and 3 control cows receiving saline solution came into estrus 13 days after administration (21 days after the preceding estrus). Progesterone levels in 3 randomly selected cows were reduced from 6.3, 6.3 and 2.6 ng/ml on the day of chitin administration to 0.3, 0.2 and 0.2 ng/ml, respectively, 6 days after administration. In addition, many leucocytes were detected in uterine mucosal biopsy specimens 2 to 3 days after chitin administration. In experiment 3, estrus was induced in 5 cows with endometritis 6-8 days after chitin administration and the endometritis was improved with the disappearance of pus. Normal embryos were obtained in 2 of 4 cows (8/12 ova; 75%) that received superovulatory treatment during the estrus cycle induced by chitin. These findings suggest that the intrauterine injection of chitin can induce estrus and subsequent ovulatory response by its therapeutic effect on endometritis in cattle.