Duodenoscopic examination of a patient with Whipple's disease revealed that the duodenal mucosa appeared to be partially covered with a yellow-white material. On closer inspection, however, this was found to consist of enlarged villi interspersed with normal-looking mucosa. Histologically these enlarged white villi were shown to contain a heavy accumulation of lipid and typical PAS positive macrophages. The duodenal mucosa was endoscopically normal and histologically showed only a few PAS positive macrophages one year after instituting antibiotic therapy.