The gastroduodenal mucosa of 30 healthy dogs was examined by endoscope after 7 days of oral non-steroidal anti-inflammatory drug administration. The dogs were divided into five groups. One group received ketoprofen (1 mg/kg every 24 h), one group copper-indomethacin (0.2 mg/kg every 12 h), one group 1 mg of prednisolone and 200 mg of cinchophen (1 tablet per 20 kg every 12 h), one group aspirin (15 mg/kg every 12 h) and one group gelatin (I capsule every 12 h).