Total (active + diffusion) absorption of leucine from the entire small intestine of rats or from segments of upper jejunum and lower ileum was unaffected by chronic ethanol feeding for 4 weeks. However, because of ethanol-induced mucosal atrophy, specific absorption (expressed per g dry weight of mucosa) was almost doubled in ethanol-fed rats. In the upper jejunum, the active component of leucine uptake was significantly greater in ethanol-fed rats (72% vs. 52%), whereas in the lower ileum the relative contributions of active uptake and diffusion were unaltered. We propose that the increase in active uptake in the upper jejunum is the result of a higher concentration of aged enterocytes having a greater transport capacity at the villus surface.