Male rats about 60 days old and weighing 120-150 g. were fasted in individual cages for 48 hrs. The pylorus was then ligated under ether and the fasting continued. Marked ulceration developed uniformly in the rumen in 7-9 hrs. It was reduced or prevented with a sufficient dose, by any of several routes, of an antiulcer substance from human urine. This may be adapted as a rapid assay method for any hormonal antiulcer agent, and to evaluate anti-secretofy agents.