The therapeutic effects on gastric ulcer and side-effects of 5,11-dihydro-11[(4-methyl-1-piperazinyl)acetyl]-6H-pyrido[2,3-b][1,4]benzodiazepin-6 one-dihydrochloride (pirenzepine, LS519), a new antiulcer drug, were investigated in 15 medical institutes by a double-blind controlled clinical study, using trans-3,7-dimethyl-2,6-octadienyl-5,9,13-trimethyltetradeca-4,8,12-trienoate (gefarnate) as the standard drug. 321 subjects were studied, 11 of whom were excluded, and analysis was carried out on the remaining 310 subjects. The final improvement rate (after 8 weeks of treatment) of the pirenzepine-treated group was significantly higher than that of the gefarnate-treated group. Cumulative healing rates based on endoscopic examination after 4, 8 and 12 weeks of treatment were 23, 71 and 76%, respectively, for the pirenzepine group and 20, 51 and 60%, respectively, for the gefarnate group, with statistical significance, especially after 8 and 12 weeks of treatment. Of the subjective symptoms, the improvement rates of epigastric pain on fasting and other occasions in the pirenzepine group were significantly higher than in the gefarnate group after 1 week of treatment. As for the global utility rate, pirenzepine showed significantly higher rates than gefarnate. Stratified analysis showed the excellent therapeutic effect of pirenzepine on ulcer lesion under various conditions, especially under difficult healing conditions, suggesting a broad spectrum of indications for the drug in clinical use. Neither pirenzepine nor gefarnate showed side-effects serious enough to require withdrawal of medication. Virtually the only side-effect encountered during pirenzepine administration was slightly dry mouth in 7.3% of the subjects.