In an effort to develop new types of antiulcer agents, we synthesized a series of novel 2-[w- (thioureido) alkyl]-and 2-[w-(cyanoguanidino) alkyl]-3 (2H)-pyridazinone derivatives. All target compounds were evaluated for gastric antisecretory activity in the pylorus-lygated rat by the method of Shay, and selected compounds were evaluated in the stress-induced ulcer test in rats. Structure-activity relationships were established. Two series of the compounds ...