The effect of endogenously stimulated gastrin on serum insulin level was investigated in 7 normal subjects. Glycine by mouth was chosen as gastrin releaser. The glycine drink caused a significant rise of serum gastrin and insulin levels either in the fasting state or during glucose stimulation. However, serum insulin response of same magnitude occurred when stimulation of gastrin secretion was prevented to occur by infusing glycine into the duodenum. The results suggest that post-glycine rise in serum insulin was not mediated by endogenous gastrin release.