Delta9-Tetrahydrocannabinol (THC) inhibited ulcer formation in the pylorus-ligated rat (Shay rat test). However, this antiulcer activity of THC was substantially less than for the anticholinergic substance tridihexethyl chloride both in terms of degree of activity and potency. In addition, the results of the present study suggested different mechanism(s) of action for the antiulcer effects of these substances.