Raman spectroscopy was applied to monitor the growth of diamond in different plasma-assisted chemical vapour deposition reactors. A gated, multichannel detection system was used to discriminate against the high level of background radiation produced by the plasma and the hot substrate. As a result, Raman spectra could be taken during diamond growth without interruption of the process. The ability to detect and distinguish between diamond and non-diamond phases during film growth is demonstrated. A sufficient signal-to-noise ratio in the spectra was achieved for stress formation to be observed.