The role of cortisol in the development of gastric function was investigated in the fetal pig. Pregnant sows (term = 114 +/- 2 days, n = 10) were anaesthetized (pentobarbitone) and osmotic minipumps containing either saline or cortisol inserted subcutaneously into fetuses at 82-84 (n = 11) or 91-96 (n = 14) days gestation. Six days later the infused pigs were removed by Caesarean section and the stomach and its contents collected for analysis. Samples were also obtained from unoperated (control) fetal pigs (n = 51) removed under anaesthesia at intervals from 70 days gestation until term. The concentrations of acid in gastric fluid, gastrin in plasma and antral tissue (bioactive as well as precursor forms), and cobalamin(CBL)-binding proteins in fundic tissue were low in control pigs until 100 days gestation. During the last 2 weeks before term, large increases occurred in gastric fluid acidity (from pH 6-7 to pH 3 at birth), plasma amidated gastrin (from 10 to 90 pM) and CBL-binding protein concentration (from 10 to 80 pmol (g fundus)-1). These changes occurred in parallel with a surge in plasma cortisol (from 20 to 200 ng ml-1). Immature fetuses infused with cortisol had significantly higher gastric acidity, plasma amidated gastrin, and concentration of CBL-binding proteins than the corresponding control fetuses (P < 0.05). Across age and treatment groups, significant correlations were found between log10 plasma cortisol values and the above parameters (r = 0.59-0.76, P < 0.01). The results suggest that endogenous cortisol secretion stimulates the secretion of gastric acid, gastrin and CBL-binding proteins in the prenatal period of the pig.