In Northern blots of total cellular and poly(A+) RNA isolated from rat liver, renal cortex, spleen, and brain probed with a full-length cDNA encoding the hamster alpha 1-adrenergic receptor, hybridization was observed to two distinct mRNAs, at approximately 3.3 kb and approximately 2.7 kb. Only the approximately 2.7 kb mRNA species was visualized in Northern blots of total cellular and poly(A+) RNA isolated from cardiac ventricular muscle. From screening a rat heart cDNA library with the full-length hamster alpha 1-adrenergic receptor cDNA, a 632 base pair cDNA was isolated. Based upon its high degree of identity, 86% at the nucleotide level, with the hamster alpha 1-adrenergic receptor cDNA, this cDNA was considered to include the 3' end of the rat alpha 1-adrenergic receptor. When used as a probe in Northern blots of liver RNA, both the approximately 3.3 kb and approximately 2.7 kb mRNAs were visualized. Both mRNA species were expressed in fetal as well as adult liver, but steady-state levels of each gene transcript were approximately 3-fold higher in adult compared to fetal liver. Finally, results from Southern analysis of restriction enzyme fragments of genomic DNA suggest that the two gene transcripts may be products of a single gene.