Samples of discs and disc attachments were extracted by dissociative methods and the resultant collagenous residues cleaved with cyanogen bromide. Soluble peptides thus released were characterized by their electrophoretic mobility following SDS-PAGE and by Western blot staining with specific antibodies against type I and type III collagens. Type III collagen was identified in samples taken from the posterior discal attachments. This may explain why this disc is prone to detachment and internal derangement and the high incidence of patients with temporomandibular joint dysfunction.