In the past it has been proven difficult to separate and characterize collagen from muscle because of its relative paucity in this tissue. The present report presents a comprehensive methodology, combining methods previously described by McCollester [(1962) Biochim. Biophys. Acta 57, 427-437] and Laurent, Cockerill, McAnulty & Hastings [(1981) Anal. Biochem. 113, 301-312], in which the three major tracts of muscle connective tissue, the epimysium, perimysium and endomysium, may be prepared and separated from the bulk of muscle protein. Connective tissue thus prepared may be washed with salt and treated with pepsin to liberate soluble native collagen, or can be washed with sodium dodecyl sulphate to produce a very clean insoluble collagenous product. This latter type of preparation may be used for quantification of the ratio of the major genetic forms of collagen or for measurement of reducible cross-link content to give reproducible results. It was shown that both the epimysium and perimysium contain type I collagen as the major component and type III collagen as a minor component; perimysium also contained traces of type V collagen. The endomysium, the sheaths of individual muscle fibres, was shown to contain both type I and type III collagen as major components. Type V collagen was also present in small amounts, and type IV collagen, the collagenous component of basement membranes, was purified from endomysial preparations. This is the first biochemical demonstration of the presence of type IV collagen in muscle endomysium. The preparation was shown to be very similar to other type IV collagens from other basement membranes on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and was indistinguishable from EHS sarcoma collagen and placenta type IV collagen in the electron microscope after rotary shadowing.