The interleukin-3 receptor is composed of a ligand-specific Lu subunit (IL-3R alpha) and a beta subunit (beta(c) or beta(IL3)). Here we report the cloning of a rat brain cDNA transcript with significant homology to IL-3R alpha, which we have termed CYRL, for CYtokine Receptor-Like protein. A number of conserved motifs identify CYRL as a member of the alpha family of cytokine receptor subunits, but the extracellular domain was too divergent from the mouse IL-3R alpha sequence to suggest that CYRL is the rat ortholog of IL-3R alpha. CYRL mRNA expression by Northern blotting was highest in the testis, intermediate in the lung, and modest in spleen, brain, and heart. Antibodies generated against the extracellular domain of CYRL specifically labeled a broad immunoreactive band of M-r similar to 50,000 in membrane fractions of testis, lung, and spleen. CYRL appears to be a novel cytokine receptor alpha-subunit of unknown function and with no defined ligands.