KC, the product of an immediate early gene induced in mouse fibroblasts by platelet-derived growth factor, was synthesized as a recombinant protein in Escherichia coli and binds with 0.8 nM affinity to mouse neutrophils. Human neutrophils also bind recombinant KC at a site competitive with human interleukin (IL8) and Gro-alpha/MGSA, consistent with binding at the IL8 type B receptor (IL8RB). The cDNA corresponding to human IL8RB hybridizes strongly with two restriction fragments in murine genomic DNA, representing candidate receptor genes for KC. Molecular cloning of both mouse genomic DNA and neutrophil exudate cell cDNA libraries yielded a receptor with approximately 68% sequence identity to both the human IL8 type A and B receptors. Transient expression of the murine receptor cDNA in COS cells conferred binding ability to KC and a related gene product, macrophage inflammatory protein-2 (MIP-2) with high affinity (approximately 5 nM). Human IL8 was a poor agonist for this expressed receptor (Kd = approximately 400 nM). The potent activity of human IL8 on mouse polymorphonuclear neutrophils is not consistent with binding on the cloned receptor and suggests that murine homologues of IL8 and an IL8 type A receptor remain to be identified. Our data indicate that KC is the murine homologue of human Gro-alpha, and the KC receptor is an IL8 type B receptor homologue capable of binding both KC and macrophage inflammatory protein-2 with high affinity.