We mapped the human (RECA) and mouse (Reca) homologs of the yeast RAD51 and Escherichia coli recA genes to human and mouse chromosomes by direct R-banding fluorescence in situ hybridization. This gene was assigned to human chromosome 15q15.1 and to mouse chromosome 2F1, respectively. This is the first report on the precise localization of this gene to human and mouse chromosomes. This gene was mapped to a region on human chromosome 15q15.1 and mouse 2F1 that is believed to be a conserved syntenic group.