This study was made to determine the extent of absorption of chlorophyll phytol from the intestine of man, and the importance of chlorophyll as a source of the phytanic acid that accumulates in Refsum's disease. Uniformly (14)C-labeled pheophytin a (the Mg-free derivative of chlorophyll a) was fed to normal human subjects and to patients with Refsum's disease. Feces were collected and analyzed. In all subjects, 90-95% of the administered radioactivity was recovered in the feces, still largely in the form of pheophytin a. The phytol radioactivity recovered in the feces averaged about 95% of that in the administered material, which indicates that there had been little absorption of the phytol moiety. Similarly, after 250 g of cooked spinach had been fed to a normal subject, almost the entire phytol content was found in the feces. Less than 5% of the ingested spinach phytol was accounted for in the thoracic duct lymph of another subject. It was concluded that not more than about 5% of the ingested chlorophyll phytol is absorbed by man, whether normal or afflicted with Refsum's disease. On this basis we conclude that the major portion of the phytanic acid that accumulates in Refsum's disease could not be derived from dietary chlorophyll.