We examined the capillaries in muscle biopsy specimens from two patients with Ullrich's disease with collagen VI deficiency by light and electron microscopy. Collagen VI plays an important role in platelet aggregation for binding von Willebrand factor. Using immunohistochemistry, collagen VI was shown to be absent on capillaries from patients with Ullrich's disease, while von Willebrand factor, collagen IV, and vascular endothelial growth factor were normally expressed. Electron microscopy revealed narrow lumens, large nuclei in endothelial cells, and fenestration of a capillary. The number of pinocytotic vesicles per unit endothelial cytoplasm was increased. The cytoplasm of endothelial cells was strongly stained with uranyl acetate and lead citrate. Replication of the capillary basement membrane was observed. On the other hand, easy bleeding and coagulation were not observed in the two patients. These findings suggested that the collagen VI deficiency might have caused the electron microscopic changes of capillaries, while the function of the capillaries is apparently retained.