This study examined the relationship between healing of acetic acid-induced chronic gastric ulcer and connexin formation. In addition, the effect of anti-ulcer drugs on ulcer healing and the presence of connexin was investigated. In a rat model, acetic acid-induced gastric ulcers were healed without administration of drugs after 14 days. Appearance of an electrophoretic connexin 32 band was observed 7 days after ulcer induction. Administration of cimetidine (3 mg/day) promoted ulcer healing, i.e., ulcers were healed 12 days after ulcer induction, 2 days earlier than the control. The appearance of a connexin 32 band in electrophoresis was observed on the fourth day after ulcer induction. Administration of cimetidine at a higher dose further promoted ulcer healing and the connexin 32 band was more strongly visible. After administration of i.p. 2 nM EGF, acetic acid-induced gastric ulcers were healed 12 days after ulcer induction and the appearance of connexin 32 was observed on the fourth day after induction. These results indicate that connexin 32 is related to the healing of acetic acid-induced gastric ulcers.