SummaryThirty-one premature infants who required nasojejunal feeding were evaluated for pancreatic exocrine function before and after feeding of milk-based or soy-based formulas for 30 days. The two groups were well matched for age and birth weight (about 1.5 kg). At birth, all infants had high basal secretion of trypsin and chymotrypsin, but low lipase and no amylase activity. Additionally, there was no response to pancreozymin (CCK). After 30 days of feeding with either soy or milk-based formulas, both groups showed a similar increase in body weight (to 1.8 kg) and basal secretion of trypsin, chymotrypsin, and lipase and failure to secrete amylase. The group that was fed milk-based formula failed to respond to CCK and secretin administration. Thus, soy- and milk-based formulas result in similar weight gain and similar basal pancreatic enzyme secretion while feeding with soy-based formula selectively increases the trypsin and lipase response to CCK.