The effect of a 75-percent resection of the proximal small bowel on sucrase and lactase activities in the remaining intestine was studied. Eight weeks after surgery, adaptation resulted in hyperplasia of intestinal mucosa to the point that its weight in the control and experimental rats matched each other. Similarly, total sucrase activity of the entire duodeno-jejunal-ileal remnant in the experimental animals (16.7 ± SD 4.3) equalled the total sucrase activity of the entire intact intestine in the controls (16.5 ± 2.4). In contrast to sucrase, lactase activity did not increase in the experimental rats. This is thought to be at least partly due to a lack of substrate induction of this enzyme.