Murine interleukin‐5 (IL‐5) is known to play an essential role in Ig production of B cells and proliferation and differentiation of eosinophils. Here, we have isolated cDNA clones encoding a murine IL‐5 receptor by expression screening of a library prepared from a murine IL‐5 dependent early B cell line. A cDNA library was expressed in COS7 cells and screened by panning with the use of anti‐IL‐5 receptor monoclonal antibodies. The deduced amino acid sequence analysis demonstrates that the receptor is a glycoprotein of 415 amino acids (Mr 45,284), including an N‐terminal hydrophobic region (17 amino acids), a glycosylated extracellular domain (322 amino acids), a single transmembrane segment (22 amino acids) and a cytoplasmic tail (54 amino acids). COS7 cells transfected with the cDNA expressed a 60 kd protein that bound IL‐5 with a single class of affinity (KD = 2–10 nM). FDC‐P1 cells transfected with the cDNA for murine IL‐5 receptor showed the expression of IL‐5 binding sites with both low (KD = 6 nM) and high affinity (KD = 30 pM) and acquired responsiveness to IL‐5 for proliferation, although parental FDC‐P1 cells did not show any detectable IL‐5 binding. In addition, several cDNA clones encoding soluble forms of the IL‐5 receptor were isolated. Northern blot analysis showed that two species of mRNAs (5.0 kb and 5.8 kb) were detected in cell lines that display binding sites for murine IL‐5. Homology search for the amino acid sequence of the IL‐5 receptor reveals that the IL‐5 receptor contains a common motif of a cytokine receptor family that is recently identified.