Beagle dogs were anesthetized with pentobarbital-Na, and waxed silk was tightened around the under cut area of the dental necks of both postmolar teeth in the upper jaw. One week later, remarkable signs of gingivitis became apparent, and gingivitis was confirmed histologically. Prozime-10 (P-10, a proteolytic enzyme) and indomethacin were givin either orally in enteric-coated capsules or parenterally (intravenously or subcutaneously) for 7consecutive days. The thickness of gingiva and the volume of exudate in the gingival poket were measured before the operation, 7days after silk ligation and after the completion of the drug administration. The effect of test drugs was evaluated in relation to these changes. Oral administration of 12.5mg/kg P-10 was quite effective in alleviating the inflammatory signs. Indomethacin (5mg/kg, p.o.) was slightly less effective, but significantly effective. In all cases of indomethacin administration, mucous diarrhoea was observed, and in some cases a visible amout of blood was mixed in the stool. No such sign was noted with P-10. The formation of granular tissue in the lamina propria of mucosa facing the waxed silk was noted characteristically in histological examinations of swollen gingiva. However, neither granular tissues nor any signs of inflammation were observed after P-10 administration.