1. Prostaglandin A-, prostaglandin E-and prostaglandin F-like substances were determined radioimmunologically in antral biopsy material obtained by endoscopy.
2. In patients with gastritis, the concentrations of prostaglandin (E + A)-like substances were six times as high and of prostaglandin F-like substances twice as high as in normal subjects. In chronic atrophic gastritis, the concentrations of prostaglandin (E+A)-like material was four times as high as in normal subjects whereas prostaglandin F-like material remained unchanged. In acute gastric ulcer, prostaglandin (E+A)-like material reached concentrations four times higher than in normal subjects, accompanied by a fivefold increase of prostaglandin F-like substances. After healing of the gastric ulcer, prostaglandins returned to normal values.
3. There was no correlation between gastrin and prostaglandins in all biopsy specimens.