The influence of a d.c. substrate bias on the properties of WTi and WTi-N films deposited by r.f. magnetron sputtering has been studied. The bias voltage was varied from 0 to -200 V. The WTi films structure is b.c.c. W with the presence of the h.c.p. Ti phase at low bias (0 to -50 V). For the WTi-N films, the structure is f.c.c. TiN at low bias and b.c.c. W+f.c.c. TiN at high bias (-100 V to -200 V). Both films exhibit the columnar morphology. The titanium fraction in the films is lower than in the target and decreases when the bias increases owing to a titanium preferential resputtering caused by the ion bombardment of the substrate. The same behaviour is found for the film resistivity which diminishes when the bias is increased whereas the crystallite size increases. The microstrains have a more complex variation with the bias.