Human FcalphaRI (CD89) is a myeloid-specific IgA Fc receptor encoded in the leukocyte receptor complex. Thus far, no gene coding for FcalphaRI has been identified in mice. Here, we show that, unlike mice, rats have the gene ( Fcar) coding for FcalphaRI. The rat Fcar gene has an exon-intron structure essentially identical to that of the human counterpart and is encoded in the leukocyte receptor complex on Chromosome 1. Southern blot analysis using the rat Fcar as a probe revealed hybridizing bands in Chinese and Syrian hamsters and gerbils, but not in mice, indicating that Fcar was lost in the lineage leading to mice after the divergence of rats and mice. Identification of FcalphaRI in rats should facilitate the elucidation of the in vivo role of this receptor.