Abstract The structural analysis by convergent-beam electron diffraction (CBED) of two new ternary phases Ni(P,Ge)x where x ≈ 1 and 2 is described. One phase, with approximate composition NiP0·6Ge0·2 and initially identified within metal contacts to InP millimetre-wave devices, contained an incommensurate displacive modulation of a NiAs-type subcell (a = 3·42 Å c=4·89 Å). Two related parallel wave-vectors q1 = (1/3 + δ)g and q 2 = (1/3 - 2δ)g were observed, where g = a∗ + b∗ and δ varied between 0·012 and 0·019 in adjacent domains defined by the three possible 〈 1120〉 directions for q. The domains were comparatively large (0·5–5·0 μm) and were separated by polygonal boundaries parallel to the {1120) and {1100} planes. Large-angle dark-field CBED patterns taken around clusters of incommensurate reflections were used to recognize dynamical one- and two-dimensional diffraction routes contributing to the intensities of q1 and q2 and to assign primarily transverse and longitudinal characters to the wave-vectors, respectively. The second phase, with approximate composition NiP1·8Ge0·2 was a marcasite, whereas binary NiP2 crystallizes in either pyrite or monoclinic forms. The lattice parameters (a=4·46 Å b=5·54 Å c=3·41 Å, space-group Pnnm) and the anion 4(g) parameters (x=0·197, y=0·379) were measured on the [111] zone axis from the geometry and intensities of first-order Laue zone reflections. Bond lengths are compared with the almost isoelectronic FeS2 compounds, and the effect of Ge substitution in Ni–P binary compounds is discussed.