We have isolated a 2.1-kb cDNA clone from a human placental library encoding part of the α2 chain of collagen IV, a major structural protein of basement membranes. The DNA sequence encodes 446 amino acids in the triplehelical domain plus the 227 amino acids of the carboxy-terminal globular domain. The latter structure is composed of two homologous subdomains and is highly conserved between the α1 and α2 chains. The triple-helical domain contained seven interruptions of the Gly-X-Y repeat and these interruptions were in general larger than their counterparts in the α1 chain. DNA from human rodent hybrid cell lines was analyzed under conditions in which there was no cross-hybridization of the α2(IV) cDNA probe with the gene for the α1(IV) collagen chain. An Eco RI fragment characteristic of the α2 chain had a concordance of 0.97 with chromosome 13. This result was confirmed and extended with in situ localization of the gene at 13q34. Since the α1(IV) gene has previously been localized to 13q34, the two type IV collagen genes reside in the same chromosome region (13q34), possibly in a gene cluster. The presence of the genes for type IV collagen chains on chromosome 13 excludes a primary role for these genes in adult polycystic kidney disease and X-linked forms of hereditary nephritis.