Abstract 1. 1. Active absorption of d-glucose by intestinal segments of Citellus tridecemlineatus was shown using in vitro preparations where the starting concentration was 1 mg/ml on each side of the intestinal wall. 2. 2. Concentration gradients across the intestinal wall were measured after 1 hr of incubation at 37°C and the rate of transport of d-glucose from the mucosal to the serosal medium ranged from 23 ± 6 to 48 ± 7 μmole/g dry wt./hr. 3. 3. The various areas of intestine examined, i.e. duodenum, jejunum and ileum, were comparable in active absorption characteristics. 4. 4. The intestine, in vitro, showed a marked ability to absorb, accumulate and retain d-glucose.