The effects of clonidine, UK-14,304, noradrenaline, para-aminoclonidine and phenylephrine were examined on the acid secretory response of the rat isolated gastric mucosa preparation to electrical field stimulation. Clonidine, UK-14,304, noradrenaline and para-aminoclonidine but not phenylephrine (10 microM) reduced the response of the gastric mucosa stimulated at 2.5 Hz; gastric mucosae stimulated at higher frequencies were insensitive to the action of these alpha 2-adrenoceptor agonists. The inhibitory effect of the selective alpha 2-adrenoceptor agonist UK-14,304 was antagonized by idazoxan but not by prazosin. These findings indicate that clonidine and other alpha 2-adrenoceptor agents inhibit the acid secretory response of the rat gastric mucosa to electrical field stimulation by an action at alpha 2-adrenoceptors, which are probably located on cholinergic nerve terminals.