Growth and functional maturation of porcine small intestine was characterized in relation to stage of perinatal development. Fatty acid binding activity of specific low molecular weight, cytosolic proteins (FABPs) was measured in the small intestinal mucosae of young pigs. Intestinal mucosa mass, soluble protein content, DNA content and oleic acid-binding capacity were determined for pigs (n=4) at -4, 2, 4, 7, 14, 22, 28 and 35 days of age. FABP activity of mucosa from the proximal half of intestine displayed a cubic pattern of change (P<.01) with age, increasing from 15.2 nmol oleic acid bound at -4 days to 542.1 nmol bound at 14 days. Oleic acid-binding decreased to 240 nmol at 22 days (day 1 postweaning) but remained elevated above preweaning values at day 28. Distal-region small intestinal FABP activity corresponded to 13.5 nmol oleic acid bound at -4 days, increased to 124.3 nmol bound at day 7, and decreased to 103.0 nmol bound at day 14. Immediately postweaning, distal-region intestinal FABP activity increased three-fold relative to the day 14 values. Proximal intestine FABP activities exceeded distal intestine activities for all days except at day 22. Total FABP activity, adjusted per mg DNA, exhibited a nine-fold increase in the proximal region of the small intestine between -4 days and day 7. The developmental variation in intestinal FABP activity suggests that FABPs may represent markers of neonatal intestinal differentiation and lipid absorptive capacity in the neonate.