The determination of suck-swallow patterns and esophageal motility were performed on 40 premature infants between 1,700 and 2,500 gm birth weight. After initial mouthing, two types of suck-swallow patterns were noted. The first, "the immature suck-swallow pattern" consisted of a rate of 1 to 1.5 sucks per minute and consisted of short sucking bursts preceded or followed by swallows. The second, "the mature suck-swallow pattern" was characterized by bursts of over 30 sucks, and a rate of 2 per second. Swallows occurred frequently during sucking bursts. The smallest premature infants had poor penistalsis in the body of the esophagus and did not attain a "mature suck-swallow pattern" until after peristalsis had become propagative. It is postulated that the "immature suck-swallow pattern" prevents the delivery of a large amount of fluid which could not be handled by an esophagus which has not yet developed the ability for adequate peristalsis.