Type VI collagen was once considered a minor collagen, but now it is known as a major component of the extracellular matrices of most tissues. Type VI collagen tetramers aggregate into beaded filaments with repeats of approximately 100 nm, and the beaded filaments align laterally to form type VI collagen periodic fibrils by incubation with acidic ATP solution. Polyanionic ATP could cause lateral alignment of type VI collagen beaded filaments. Since the periodic structure is observable by transmission electron microscopy, we can examine the tissue distribution of type VI collagen by ATP treatment. Moreover, the interaction of type VI collagen with other extracellular matrix components can be examined by combining ruthenium red (RR) staining, which specifically interacts with tissue glycosaminoglycans (GAGs), with the ATP treatment. I here describe the localization and possible function of type VI collagen examined in our laboratory. After ATP incubation, numerous type VI collagen periodic fibrils appeared closely associated with striated collagen fibrils (mouse cornea and fibrous layer of mandibular condyle), with trophoblastic and endothelial basal lamina (human placenta), or with cell surface of fibroblasts (mouse tendon) and synovial cells (mouse synovium). The dark bands of the type VI collagen periodic fibrils were stained by RR, indicating the association of proteoglycans (PGs)/GAGs with this collagen. If the mouse corneal tissue was digested with chondroitinase ABC or testicular hyaluronidase prior to ATP treatment, type VI collagens were segregated to form periodic structures apart from striated collagen fibrils. In the mouse mandibular condyle, hyaluronidase digestion before ATP treatment caused unmasking of type VI collagen.(ABSTRACT TRUNCATED AT 250 WORDS)