Laminin, a substrate adhesion molecule in vertebrates, is a large glycoprotein complex in basement membranes that promotes cell adhesion, cell migration, and neurite outgrowth. Here we report on the cloning of the genes encoding the three subunits of Drosophila laminin. Sequence analysis of cDNA clones encoding the Drosophila B1 chain reveals a multidomain structure similar to that of its mouse homolog. The Drosophila sequence has only 25% amino acid identity with the mouse sequence in domains I, II, and IV. However, in one of the putative collagen-binding regions (domain VI) and the two cysteine-rich domains of EGF-like repeats (domains III and V), the amino acid identity between these two evolutionarily distant species jumps to 55%. Moreover, the number, length, and unique amino acid sequences of each of the 13 EGF-like repeats are highly conserved between Drosophila and mouse, suggesting that each may serve a unique function in protein-protein interactions.