The influence of weaning, at either 4 or 6 weeks of age, on the maturation of the exocrine pancreas was studied in naturally reared Swedish Landrace pigs that had no access to solid food. The pigs were surgically fitted with chronic catheters at 3 weeks of age, permitting periodic sampling of pancreatic juice and blood in conscious animals < or = 4 weeks after weaning. During the suckling period, pancreatic fluid and enzyme secretion remained low, both before (preprandial) and after (postprandial) milk ingestion. After weaning at 4 or 6 weeks of age, juice secretion, output of total protein, and levels of different hydrolases (amylase, trypsin, lipase, and carboxylester lipase) and the cofactor colipase all increased markedly postprandially. Moreover, after weaning, the plasma insulin level increased postprandially. This did not happen before weaning, although blood glucose levels always rose after feeding. The data showed a relationship between the time of weaning and the induction of exocrine pancreatic maturation in pigs. This finding implies that postnatal development of pancreatic function is triggered by the dietary change from sow milk to dry solid food. In contrast, the age of the pig appears to be of minor importance, since weaning at either 4 or 6 weeks of age gave a similar result.