Composite films containing tungsten clusters dispersed in an organosilicon matrix have been deposited by simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane-O-2-Ar mixtures and r.f. sputtering of a tungsten target. The effect of plasma conditions on the deposition process and film composition has been investigated. It is shown that actinometry can conveniently be utilized as an in-situ process parameter.