We evaluated gastrointestinal structure and function in 13 hemizygous males and 17 heterozygous females, five to 67 years old, from four kindreds with Fabry's disease. Gastrointestinal symptoms, noted in 62% (8/13) of the males and 29% (5/17) of the females, were present prior to the diagnosis of Fabry's disease in five patients; were discovered at the time of study in six patients and were associated with multiple other symptoms in two patients. Serum protein, albumin, folate, Vitamin B12, calcium, phosphorous, cholesterol and iron were normal in all 30 patients. Xylose absorption was normal in 2/2 males and 13/13 females studied. HLA B8 antigen was present in none of the males and 2/17 females. Peroral duodenal (one male), jejunal (six males, two females) and rectal (one male) biopsies on light microscopy demonstrated a normal villous pattern and luxol-fast blue positive "foamy" cell deposits in all males, while no deposits were visualized in the females. In all males and females studied, electron microscopic examination showed electron dense, intralysosomal "zebra-like" (0.5-0.75 micrometer.) bodies in the vascular endothelial and perithelial cells and in the cytoplasm of the small unmyelinated neurons, and perineurial cells. Despite the frequency of gastrointestinal symptoms, both malabsorption and celiac disease were absent.