We studied epitaxially grown single-crystalline chemically disordered ultrathin NixPd1-x alloy films on Cu3Au(100) by means of photoemission using magnetic circular dichroism in the angular distribution. We clearly observe a well-defined three-dimensional band dispersion in 15 monolayer films. On the basis of relativistic selection rules, this dispersion can be related to specific electronic states. Since the spin–orbit coupling (ΔEso) is smaller for Ni than for Pd, the alloy will assume an average value. We find that this average spin–orbit coupling clearly shows up in the electronic structure and correlates directly to the composition of the NiPd alloy film. The results are discussed in terms of a simple qualitative model. © 2001 American Institute of Physics.