Type V collagen has already been shown, in many immunohistochemical studies, to be widely distributed in connective tissues. Its supramolecular structure, however, has been unclear. We demonstrate that the major aggregates formed from type V collagen solution in vitro are fine fibrils with a D-periodic banding pattern. Further, by using the immunogold labeling method, we find that these fibrils react strongly with anti-type V collagen antibody. Electronmicroscopic examination showed three kinds of aggregate: fine fibrils with periodic banding pattern, fine fibrils without banding pattern, and non-fibrillar materials. Both striated and nonstriated fibrils, when incubated with rat polyclonal anti-human type V collagen IgG followed by incubation with 15 nm-gold conjugated goat anti-rat IgG, were labeled with colloidal gold. We conclude that type V can be classified as a fibrillar collagen. Also, from the present findings together with previous studies, we believe type V collagen may exist in vivo in various connective tissues as fine fibrils with a 67 nm-periodic banding pattern, by itself, or with type I or type III fibrillar collagen, being located between, and connecting the basal lamina and interstitial collagen fibers.