The gastrointestinal protective action of SCH 12223 [3-(n-butyl)-4-hydroxy-1-phenyl-1,8-naphthyridin-2(1H)-one hydrate, sodium salt] against various noxious stimuli was characterized in rats. SCH 12223 inhibited the ethanol-induced gastric lesions when given p.o. (0.3-3 mg/kg) or i.v. (1 and 3 mg/kg). Indomethacin pretreatment (10 mg/kg p.o.) did not interfere with this effect. SCH 12223 was also active p.o. in five gastric erosion models: aspirin (1-10 mg/kg), aspirin + acid (1-30 mg/kg), indomethacin (1-10 mg/kg), stress (1 and 3 mg/kg) and reserpine (0.3-10 mg/kg)-induced erosions. The compound lacked antisecretory activity in the pylorus-ligated rats (10 mg/kg p.o.) but increased total gastric mucus (N-acetylneuraminic acid measurements) (1-10 mg/kg p.o.). SCH 12223 (10 and 30 mg/kg p.o.) attenuated intestinal lesions provoked by indomethacin (20 mg/kg p.o. or s.c.) and the protected animals showed better weight gain and food intake than controls. In a 38-day study, SCH 12223 also improved survival from indomethacin lethality (6 of 16 vs. 16 of 16 in the control, P less than .05). The protection cannot be attributed to changes in biliary excretion and plasma levels of indomethacin. We conclude that SCH 12223 is a unique agent which protects both gastric and intestinal epithelia from noxious stimuli, a feature shared by prostaglandins.