Morphology and function of so-called nasal "swell bodies" or "cavernous tissue" have been studied by many investigators during the past 140 years. However, many details of this interesting and peculiar tissue remained unsolved, even though this vascular system plays an important role in a variety of rhinologic disorders. The present study describes electron-microscopic details of the muscular coat of the different venous structures that form human nasal swell bodies. The specimens were taken from patients requiring removal of conchal mucosa and septoplasty; semithin and ultrathin sections were obtained and examined with the optical and electron microscopes. The histologic evaluation showed differences in the venous wall structure depending on the location of the vessels. The muscular layers were significantly thinner in those parts of the swell bodies located adjacent to the epithelium. Electron-microscopic studies enabled us to determine the cytoplasmic components of smooth muscle cells, i.e., thin filaments, glycogen granules, caveolar plasmalemmal areas, cytoplasmic dense bodies (CDB), and membrane-associated dense bodies (MADB). Another interesting feature was the varying appearance of the basal lamina of smooth muscle cells of the cavernous tissue. Based on the findings of the present study, the morphologic peculiarities of nasal swell bodies are compared and discussed with the appropriate literature. Further immunohistochemical and molecular-biological studies will have to be performed to understand the complex functional mechanism of this unique vascular system.