The ternary μ phase in the system Zr-Nb-Al has been studied by resonant powder diffraction at the Zr and Nb K-edges in order to determine the distribution of the three species on the five different sites of the crystal structure. The results are presented in comparison with those obtained for the μ phase in other systems. The comparison of the results obtained using two or three data sets in the refinement allows a discussion on the methodology.