We have isolated and sequenced a cDNA clone coding for the murine c-fms gene. The 3677 nucleotide cDNA clone codes for a protein of 976 amino acids, which has 76% and 75% homology to the v-fms and human proteins, respectively. The predicted membrane protein, c-fms, has an amino terminal signal sequence and external, transmembrane and cytoplasmic domains. The homology between murine c-fms and v-fms or human c-fms is the strongest (90%-95%) in the cytoplasmic domain and weakest (59%-63%) in the external domain. The c-fms clone was inserted into a retroviral vector containing a neomycin resistance gene and cell lines resistant to G418 were isolated. These cell lines expressed protein which was immunoprecipitated by anti-c-fms antibodies and of the same size as murine c-fms. These cells were also found to specifically bind human CSF-1.