The effect of the duodenal ulcerogen cysteamine on gastric emptying of a liquid meal was compared to that of two newly identified duodenal ulcerogens, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and mepirizole. Emptying rates after acute and chronic treatment with duodenal ulcerogens were obtained. Acute administration of cysteamine, MPTP, or mepirizole significantly delayed gastric emptying of the meal. Chronically treated rats, however, showed either no change or accelerated gastric emptying after cysteamine, MPTP, or mepirizole. Gastric emptying in chronically treated animals was faster in rats that developed the most severe duodenal ulcers. These results indicate that delayed gastric emptying instead of accelerated emptying is a more common abnormality during duodenal ulceration. After the ulcer develops, however, unaltered or accelerated gastric emptying is observed experimentally, thus suggesting that accelerated gastric emptying in duodenal ulcers is an acquired alteration. The implications that these experimental findings may have in the pathogenesis of duodenal ulcer, in light of the clinical data available, are discussed.