Diamond films were deposited by pulse-modulated magnetoactive microwave plasma chemical vapour deposition. The dependence of the deposition rate on the modulation frequency showed a strong peak at 500 Hz. The deposition rate of the pulse-modulated plasma was several times larger than that of the continuous plasma at the same microwave power. The time-averaged methyl radical (CH3) density measured by infrared laser absorption spectroscopy was also enhanced by pulse modulation; however, the CH3 density was not always proportional to the resulting deposition rate.