We report the variation of the thickness dependence of the Curie temperature for a range of ultrathin ferromagnetic alloy films. By simultaneously depositing Fe or Co and Ni on Cu(100) we produce pseudomorphic alloys with controlled stoichiometry. An analysis of the Curie temperature versus thickness curves with an empirical finite size scaling formula reveals that the Curie temperature in the thick film limit increases monotonically with Co or Fe concentration. We compare the bulk alloy Curie temperatures to those of the alloy films extrapolated from the few monolayers limit. © 1995, American Vacuum Society. All rights reserved.