The receptors for interleukin-3 (IL-3), IL-5, and granulocyte- macrophage colony-stimulating factor (GM-CSF) are heterodimers comprised of ligand specific alpha chains and a common beta chain. The genes encoding the IL-5 receptor alpha chain and the common beta chain reside on chromosome 3 and 22 respectively, while the GM-CSF receptor alpha chain gene (CSF2RA) has been mapped to the pseudoautosomal region (PAR) of the sex chromosomes, which is a 2.6-Mb stretch of homologous sequence at the tips of the short arms within which a single obligatory recombination occurs during male meiosis. We have mapped the gene encoding the IL-3 receptor alpha chain (IL3RA) to the sex chromosomes by polymerase chain reaction (PCR) analysis of human-mouse or human- chinese hamster cell hybrids, and to Yp13.3 and Xp22.3 using fluorescence in situ hybridization. To explore the possibility that IL3RA is located within the pseudoautosomal region we screened the Centre d'Etude du Polymorphisme Humain (CEPH) pedigrees for an informative-restriction fragment-length polymorphism (RFLP) that showed male meiotic recombination. Two informative CEPH pedigrees were identified that displayed this phenomenon, confirming the psuedoautosomal location of IL3RA. Using long-range restriction mapping we have found that IL3RA maps to the same 190-kb restriction fragment as CSF2RA, suggesting that a cytokine receptor gene cluster may reside in the PAR.