We investigated the preventive effect of an orally active chymase inhibitor, NK3201 (2-(5-formylamino-6-oxo-2-phenyl-1,6-dihydropyrimidine-1-yl)-N-[[3,4-dioxo-1-phenyl-7-(2-pyridyloxy)]-2heptyl]acetamide), on the adhesion formation in a hamster experimental model. Hamsters were administered orally once daily with 30 mg/kg of NK3201 or placebo from 3 days before uterus scraping to 7 days after it. A significant increase of chymase activity in the injured uterus was reduced by treatment with NK3201. The score of adhesion formations in the chymase inhibitor-treated group was significantly decreased in comparison with that in the placebo-treated group (P < 0.01). Oral administration of NK3201 may be a useful drug for prevention of peritoneal adhesion formation.