Neutral CH3radicals in a capacitively coupled rf discharge in methane have been detected with a quadrupole mass spectrometer utilizing a threshold ionization technique. The absolute density of CH3radicals was measured at pressures from 0.5 to 20 mTorr, together with the ionic composition of the methane plasma. The principal ionic species were CH+5and C2H+5, except in the low‐pressure region, suggesting the importance of ion‐molecule reactions in the plasma. The lifetime of CH3radicals in the afterglow of pulsed rf discharges was measured and explained in terms of the recombination reaction CH3+CH3→C2H6.