Nutrients are believed to have a direct trophic effect on the cells of the gastrointestinal mucosa. However, no normal constituent of the diet has ever been shown to stimulate mucosal growth when administered orally. Sham-operated and antrectomized rats were fed 20 g of powdered commercial rat pellets daily or 20 g of food containing dimethylamine (100 mumol/g food). After 7 days rats were killed and growth of the mucosa of the oxyntic gland portion of the stomach and 2-cm segments of duodenum, jejunum, and proximal colon was determined. Antrectomy resulted in significant decreases in the weight and the DNA, RNA, and protein content of all four tissues and serum gastrin levels. Feeding amines abolished the differences in the oxyntic gland and duodenal mucosa. In general, the effect of amines decreased distally. Feeding amines did not significantly alter serum gastrin levels. These data indicate that dietary amines may directly stimulate the growth of gastrointestinal mucosa. These results may explain some of the proximal-to-distal gradients described for the growth of the mucosa.