Laminin is a large basement membrane glycoprotein composed of three subunits designated the A, B1, and B2. We report here the isolation and nucleotide sequence of human laminin A chain cDNA. The nucleotide sequence spans 9505 bases and has an open reading frame encoding 3075-amino acids. The sequence covers a 77-nucleotide long 5' untranslated region and a 190-nucleotide long 3' sequence in front of the poly (A)+ tail. In analogy with the mouse A chain sequence, the deduced human amino acid sequence contains eight-distinct domains of four-globular regions, three-cysteine-rich domains and an alpha-helical region, which is though to interact with the B chains of laminin. The deduced amino acid sequence is 14-amino acids shorter than the mouse A chain sequence. Seven of these amino acids are located in the putative signal sequence. The overall identity between the sequences from the two species is 78%. The carboxylterminal globular (G) domain contains five homologous subdomains characterized by a conserved seven-amino acid repeat within each subdomain. Both human and mouse A chain are about 39% identical to the G domain of merosin, a recently discovered A chain homologue. Unlike the mouse A chain, the human A chain contains a potential cell binding sequence (RGD) in this domain. The RGD sequence that is thought to be a cryptic cell attachment site in the amino-terminal domain IIIb of mouse laminin is not conserved in the human sequence.