Uptake of retinol in the developing intestine of suckling rats (14–15 day old) and its maturation in adult rats (90 day old) was examined using intestinal everted sacs. Uptake of retinol (0.06 μM) in the jejunum of suckling and adult rats was linear for 5 min incubation and occurred at a rate of 31.20 and 6.98 pmol/g tissue/min, respectively. In both age groups, uptake of retinol (0.06 μM) was significantly higher (p< 0.01) in the jejunum than the ileum. Uptake of retinol was significantly higher (p< 0.01) in suckling rats as compared to adult rats both in the jejunum and the ileum. In both suckling and adult rats, the uptake of retinol in the jejunum was1) saturable with a Vmaxvalue of 19.78 and 6.24 nmol/g tissue/5 min and an apparentKmvalue of 16.20 and 8.19 μM, respectively,2) not affected by metabolic inhibitors, and3) partially temperature dependent (Q10= 2.51 and 1.92, respectively). The structural analogues retinal (50 μM) and retinoic acid (50 μM) did not affect the uptake of [3H] retinol (0.06 μM) whereas unlabeled retinol (50 μM) caused significant (p< 0.01) inhibition. No difference in retinol metabolism by intestinal tissue was observed in the two age groups. These results demonstrate that retinol uptake in suckling rats is similar to that of adult rats in being a passive carrier-mediated process. The results also suggest that a decrease in the number and/or activity and an increase in the affinity of the uptake system of retinol occurs with maturation. (Pediatr Res24: 481–485, 1988)