Pinacidil and diazoxide induced concentration-related relaxations of the longitudinal muscle of the mouse distal colon. The relaxing effects of pinacidil and diazoxide were unaffected by tetraethylammonium, but were antagonized by tolbutamide and glibenclamide. Relaxations provoked by nifedipine were not counteracted by the two hypoglycaemic sulfonylureas. It is tempting to suggest that the relaxation response to pinacidil and diazoxide could reflect the ability of both compounds to interfere with membrane K+ channels sharing common pharmacological properties with the K+ATP channels recently described in other tissues.