1. The rediae of P. acanthus and C. lingua and their gastropod hosts T. lapillus and L. littorea, contained substantial amounts of "free" carbohydrate and polysaccharide. The free fraction consisted of glucose and at least one other sugar probably trehalose.2. Rediae and host heptopancreas tissues absorbed exogenous glucose and incorporated significant amounts into polysaccharide in vitro.3. Glucose absorption in rediae was markedly depressed by a low concentration of phlorizin, an inhibitor of mediated transport systems. Incorporation into polysaccharide was greater in air than under nitrogen, and atmospheres containing carbon dioxide were inhibitory independent of the presence of oxygen.4. The results support the hypothesis that rediae absorb nutrients through the body surface in addition to ingestion of particulate matter into the gut. The rediae have substantial amounts of glucose available to them in vivo and the potential to absorb and utilize glucose has been demonstrated. Since the apparent rates ...