The two ternary phases W5As2.5P1.5 and Ni4Nb5P4 have been investigated by X-ray powder diffraction. Precise data for the two compounds were collected using CuKα1 radiation over the range 11°–140° 2θ. Unit cell refinements (space group I4/m) led to a=9.4729(3) Å, c=3.2414(2) Å (Dx=13.16 gcm−3) with M20=127, F30=91(0.0092,36) for W5As2.5P1.5 and a=9.9304(4) Å, c=3.5243(3) Å (Dx=7.87 gcm−3) with M20=179, F30=138(0.0068,32) for Ni4Nb5P4.