Fat digestion, absorption, and transport in the fresh water mollusc Diplodon delodontus were studied after 1 and 6 h of force-feeding 14C tripalmitoylglycerol and 1-14C palmitic acid. In a 1 h period, the mollusc was able to hydrolyze more than 50% of the triacylglycerol to free acids monoacyl and diacylglycerols. Digestion and absorption was completed before the 6 h feeding, and most of the label was eliminated. Hydrolysis occurred primarily in the stomach. The mollusc absorbed the products of hydrolysis and apparently triacylglycerol molecules, too. During the period of tripalmitoylglycerol digestion (1 h), the labeled palmitic acid was transported by the hemolymph in the free acid, monoacylglycerol, and triacylglycerol fractions that were also the principal components found in the stomach. During the post absorption period (6 h) the label was principally bound to triacylglycerols. When 1-14C palmitic acid was fed to D. delodontus, the acid was absorbed and the label transported exclusively in the free acid fraction of the hemolymph during the first hour. At 6 h ∼75% was still transported as free acid and the rest as triacylglycerol. The free palmitic acid was incorporated in the soft tissues of the mollusc and slowly esterified to triacylglycerols.