Two genomic DNA clones encoding part of the mouse epidermal growth factor (EGF) receptor were isolated: an 8.0 kb insert that hybridized with the human EGF receptor kinase domain; and a 2.4 kb insert that mapped between the kinase and 3' autophosphorylation domains of the human EGF receptor gene. The 2.4 kb insert was further digested to a 2.0 kb fragment and a 0.4 kb fragment containing 49 residues that were almost identical to the corresponding human EGF receptor sequence. Ribonuclease protection studies with mouse RNA identified three exons of 170 kb, 105 kb, and 50 kb in the 2.0 kb probe that were less homologous to the corresponding human or rat mRNAs. Northern blot hybridizations identified two EGF receptor transcripts of 10 kb and 6 kb in normal, but not EGF-nonresponsive, mouse cell lines, and a single 9.5 kb transcript in rat cells. An additional 6.5 kb transcript from rat NRK cells was identified that is related to but not transcribed from the EGF receptor gene.