Insulin and glucagon have variable effects in altering arteriovenous differences for amino acids and glucose in liver and muscle. It has not been determined whether these hormones may similarly affect intestine. Acute effects of intraarterial insulin and glucagon were evaluated in in situ, luminally cleansed ileal segments in anesthetized, fasted dogs. Insulin significantly increased th ileal uptake of valine, isoleucine, leucine, tyrosine, threonine, and serine from arterial blood: uptake of these amino acids was approximately doubled 45 min after the end of the insulin infusion. Insulin had no effect on glucose uptake or release. Glucagon decreased ileal glutamate release into mesenteric venous blood 45 min after the end of infusion but the uptake or release of other amino acids and ammonia was not changed. Glucagon did increase mesenteric blood flow acutely and caused a net release of glucose into mesenteric venous blood. The results indicate that insulin and glucagon directly after metabolism of the ileum in vivo.