The expression and activity of the apical ileal sodium-dependent bile acid transporter (asbt) was examined in the small intestine of control, pregnant and lactating postpartum rats 2, 12 and 21 days after delivery. Western analysis of brush border membrane vesicles (BBMV) prepared from different regions of the small intestine demonstrated that expression of asbt was maximal in the most distal segments for all experimental groups, was not substantially affected in pregnant and 2-day postpartum rats and was significantly increased in 12- and 21-day postpartum rats. Analysis of mRNA suggested that asbt protein was regulated at the post-transcriptional level in postpartum rats. Increased expression of asbt protein postpartum was maximal (about two-fold) in the proximal region of the ileum, consistent with a 60% increase in taurocholate (TC) transport in BBMV from the proximal ileum in rats 14-21 day postpartum relative to controls. Absorption of TC, determined from the intact proximal ileum using an intestinal loop model, demonstrated a 30% increase in TC uptake per unit weight of tissue in 14-21 day postpartum rats relative to controls. Taken together with the marked increase in intestinal mass observed at peak lactation, these data indicate a significant increase in asbt-mediated reclamation of bile acids in maternal intestine of lactating rats.