Morphine and clonidine are among the few agents reported to modulate non-adrenergic, non-cholinergic (NANC) responses in different tissues. They were therefore tested for their effect on the NANC inhibitory response in the rat gastric fundus. Neither morphine (10(-5) M), nor clonidine (10(-5) M in the presence of prazosin 10(-6) M to avoid its own relaxatory effect) modified the NANC response in the rat gastric fundus.