The Ox-44 (CD53) leukocyte antigen contributes to the transduction of CD2-generated signals in T cells and natural killer (NK) cells and has been suggested to play a role in growth regulation. The gene encoding this protein was assigned to the midportion of mouse chromosome 3 by interspecific backcross mapping and to human chromosome region 1p21-->p13.3 and rat chromosome region 2q34-->q41 by fluorescence in situ hybridization. Comparative mapping data presented in this report demonstrate conservation of synteny within the region encompassing this gene in mouse (Cd53), human (CD53), and rat (CD53).