A collagen species was isolated from the skin of 8 week-old chicks by pepsin treatment at 4 degrees C and was identified as type III collagen by analogy to human and calf type III collagen. Like human type III collagen, the type III collagen molecule from chick skin is composed of three alpha1 (III) chains which are linked together by disulfide bridges. The amino acid composition of [alpha1 (III)]3 purified by CM-cellulose chromatography and agarose-gel chromatography includes two cysteine residues per chain, and the hydroxyproline/proline ratio is greater than 1.0. The cyanogen bromide peptide pattern of [alpha1 (III)]3 on sodium dodecylsulfate acrylamide gel electrophoresis differed from that of alpha1 (I), alpha1 (II) and alpha2 chains. Segment-long-spacing crystallites from chick skin type III collagen showed the same cross striation pattern as segment-long-spacing crystallites from calf skin type III collagen. Unlike human type III collagen, type III collagen from chick skin was highly soluble in 1.0M NaCl, 0.05M Tris/HCl buffer, pH 7.5, and could not be separated from type I collagen by fractional salt precipitation. On CM-cellulose chromatography, [alpha1 (III)]3 molecules from chick skin eluted in the same position as alpha2 chains, in contrast to human [alpha1 (III)]3, which elutes in the position of beta12.