We have compared the reactivity to carbachol and noradrenaline of circular smooth muscle isolated from the human colon which was cold-stored at 4 degrees C in three different preservative solutions: Krebs bicarbonate solution (KBS), phosphate buffer solution (PBS) or minimum essential medium (MEM). Concentration-dependent contractions in response to carbachol were reduced in terms of both their sensitivity (pEC50) and reactivity (Emax), depending on the period of cold storage. The reduction was more marked when the tissue was cold-stored in either MEM or KBS than in PBS. Similar reduction of the relaxation response to noradrenaline was also observed after cold storage. It is concluded that the cold storage of surgically resected human colon in PBS for two to three days best preserved smooth muscle functions for pharmacological examinations.