This paper reviews cell surface Ags expressed on mouse hemopoietic and nonhemopoietic cells. The review will cover molecules included in the cluster of differentiation (CD) from CD1 to CD166 and lymphocyte Ag (Ly) series from Ly-1 to Ly-81 as well as some new Ags without current CD or Ly assignments. In addition to an update on mouse nomenclature, there will be a discussion of some known functions of the molecules and brief comments on the use of particular Ags for immunophenotyping of cell subsets. Several novel markers mentioned may prove useful in mouse immunology research.