Oral administration of 5-fluorouracil (5-FU) emulsion was compared experimentally with that of 5-FU aqueous solution as to the degree of absorption and tissue distribution. After oral administration of both the 5-FU emulsion and the 5-FU solution, 5-FU was detected at the highest level in both the stomach and the duodenum. This seems to suggest that 5-FU is strongly affinitive to the tissues of the gastrointestinal tract. As to the relative concentration of these two forms of the drug, the oral administration of the 5-FU emulsion resulted in a maximum value 1.5 times higher than that of the 5-FU solution. An appreciable concentration of 5-FU was maintained for a considerably long time with the administration of 5-FU emulsion. In the lymph, the maximum level of the 5-FU emulsion was three times higher than that of the 5-FU solution. The drug concentration of the 5-FU emulsion remained higher than that of the 5-FU solution through the entire duration of the experiment. Regarding the drug concentration in the regional lymph nodes, the pattern demonstrated was almost the same as in the lymph itself. It is expected that the oral administration of 5-FU emulsion may be useful as an adjuvant to the surgical treatment of gastric cancer, because of the high drug concentration resulting both in the gastrointestinal tract and in the regional lymph nodes.