Three new collagen α chains have been isolated from synovial membrane, gingiva and skin. Two of these have a similar chromatographic behaviour to the α [A] and α [B] chains described by Burgeson et al.(4) from a foetal basement membrane source but have been separated from another contaminating α chain, α [C]. The α [A] and α [B] chains are present in approximately equal amounts. They contain no detectable 3-hydroxyproline, are highly glycosylated and all sugar residues are present as the disaccharides. The percentage of hydroxylation of the lysine is of the order of 70%. Only a third of these hydroxylysine residues are glycosylated. The significance of these peptides, present in a tissue substantially free of basement membrane, is discussed.