The as-deposited state and the annealing behaviour of metastable W-Ni-C films, synthesised by non-reactive r.f. magnetron sputtering, have been studied by means of electron probe microanalysis, secondary ion mass spectrometry, X-ray diffraction, differential thermal analysis and in-situ high temperature transmission electron microscopy. The results are presented and correlated with previous studies on W-(Fe,Co)-C films. As will be shown, the as-deposited structure of the films is dependent on chemical composition and varies from crystalline to amorphous with increasing nickel content. The transformation structures produced during annealing of the films are consistent with those anticipated from the W-Ni-C equilibrium phase diagram.