Using macroscopic criteria for injury, prostaglandins have been alleged to possess potent antiulcer properties despite meager histologic evidence for this cytoprotective action. This time-sequence study used light, scanning, and transmission electron microscopy to evaluate the effects of 16,16-dimethyl prostaglandin E2 on gastric mucosal integrity after exposure to 100% ethanol. Macroscopically, virtually complete protection against injury to the glandular mucosa of the in vivo rat stomach was noted in animals receiving 10 micrograms/kg body wt of prostaglandin subcutaneously before oral ethanol administration when killed at 5, 20, and 60 min after ethanol exposure compared with oral ethanol after saline injection. On light microscopy the length of injured epithelium in prostaglandin/ethanol- and saline/ethanol-treated tissues was not significantly different at all time periods studied. Although the depth of injury extended into gastric glands in both groups killed at 5 min, the deep pit surface mucus cells in prostaglandin/ethanol mucosa were less damaged and necrotic lesions were virtually absent when compared with saline/ethanol mucosa. At 20 and 60 min, cellular injury could still be identified in prostaglandin/ethanol-treated mucosa but the depth of injury became even less pronounced over time in contrast to mucosa exposed to ethanol without prostaglandin. Scanning electron microscopy and transmission electron microscopy confirmed these differences. Despite the macroscopic findings, these results indicate that prostaglandin does not prevent superficial surface mucus cell necrosis in ethanol-exposed mucosa even though it does spare cells in the pit base. The reduction in damaged cells over time in prostaglandin/ethanol-treated mucosa, in contrast to saline/ethanol-treated mucosa, supports the hypothesis that the reepithelialization of the lamina propria is initiated by spared deep-lying pit cells.