By use of stable isotope labeled amin acid 15N-glycine the effects of truncular subdiaphragmatic vagotomy and of pyloroplasty, which are comprised in the method of bionomic gastric operations, were studied separately. The assessment of nitrogen equilibrium in rats after only truncular vagotomy, only pyloroplasty, truncular vagotomy combined with pyloroplasty, and without surgery serving as controls yielded results as following: After truncular vagotomy the 15N equilibrium was worse than in the control animals or after pyloroplasty only. The cause of that is an enhanced nitrogen loss in urine. After truncular vagotomy with pyloroplasty, though, 15N excretion in feces was significantly higher than after only pyloroplasty. It may be concluded from these results that truncular vagotomy is primarily responsible for the disturbances in protein metabolism. Pyloroplasty in combination with truncular subdiaphragmatic vagotomy also causes a higher nitrogen excretion in the feces indeed.