Binding of C1q to cell surfaces has been shown to mediate a number of biological activities including enhancement of phagocytosis and stimulation of superoxide production. Several C1q binding proteins have been proposed as candidate receptors for these functions. The 126-kDa human C1q membrane receptor, termed C1qR(p), has recently been cloned. This molecule is believed to play a role in the enhancement of phagocytosis in monocytes and macrophages, and its expression has been shown to be restricted to cells of the myeloid lineage, endothelial cells, and platelets. Here we report the isolation and genomic characterization of the murine homolog of C1qR(p). Degenerate oligonucleotide primers based on the published human sequence were used to amplify a region of the murine homolog spanning from the carbohydrate recognition domain to the fourth epidermal growth factor (EGF) domain. This fragment was used as a probe to isolate the murine gene from a 129/Sv genomic lambda library. The predicted primary protein sequence displayed 68.1% identity with the human homolog. All the major structural domains were conserved between the two molecules. The coding sequence of the murine gene was contained within two exons separated by a small intron of approximately 250 bp. The structure of the human gene was found to be similar, with the position of the intron conserved. Cloning of the murine C1qR(p) will facilitate further investigation of the physiological function of this molecule.