We used antibodies against mouse Englebreth-Holm-Swarm (EHS) tumor laminin to screen a newborn rat kidney lambda gt11 expression library and isolated three overlapping cDNA clones, termed 2b-11 (401 bp), 10-b7 (779 bp), and 2a (2,095 bp). DNA sequence analysis identified these cDNAs as encoding much of the carboxy terminal domain I/II of laminin gamma 1 chain (formerly referred to as B2e), and 1436 bp of the 3' untranslated region. In situ hybridization of fetal (E15) rat sections localized laminin gamma 1 chain mRNA primarily to meninges of the brain, auditory and peripheral nerve fibers, gastrointestinal system, and developing lung airway epithelium. Intense hybridization was also found in early nephric structures and glomeruli of fetal kidneys. In kidneys of three-day-old rats, hybridization persisted over early nephric figures, developing glomeruli, and collecting ducts, but considerably less hybridization was seen over tubules. On Northern blots of neonatal kidney RNA, the three cDNA clones hybridized to two species of 7.5 and 5.5 kb, suggesting that developing rat kidney laminin gamma 1 mRNAs are processed using two different polyadenylation signals.