We investigated the effect of 4-weeks famotidine administration (15 mg/kg/day) on gastrin cell (G-cell), somatostatin cell (D-cell) and prostaglandin E2 (PGE2) of gastric mucosa in pyloric stenosis rats. As a result, the increase of G-cell number and serum gastrin level in pyloric stenosis rats were potentiated by famotidine administration. However, the increase of D-cell number in pyloric stenosis was remarkably abolished by famotidine administration, and G/D cell ratio was increased accordingly. Moreover, famotidine administration decreased PGE2 concentration in fundic mucosa of the stomach without altering PGE2 concentration in pyloric mucosa. Our results suggested that famotidine administration in pyloric stenosis had a possibility to worsen the balance of endocrine cell kinetics in stomach, and PGE2 in fundic mucosa would play a roll on the proliferation of D-cell in pyloric stenosis.