The bimolecular rate constants, 2kt, for the self-reactions of methyl radicals and of radicals with the structures (CH3)3M·, (CH3)3MĊH2, (CH3)3MṀ(CH3)2, and (CH3)3MM(CH3)2ĊH2, where M is carbon, silicon, germanium, or tin, have been measured at room temperature in di-tert-butyl peroxide as solvent. Values of 2kt range from 1.1 × 1010 M-1 sec-1 for methyl to 1.6 × 109 M-1 sec-1 for (CH3)3GeGe(CH3)2ĊH2. The logarithms of the rate constants exhibit a surprisingly good linear correlation with the molecular weight of the radical. This is attributed to the fact that the radius for diffusion increases with increasing size of the radical while the radius for reaction remains almost unchanged. For the trichloromethyl radical in the temperature range -75 to -15°, 2kt = 1.2 × 108 M-1 sec-1, which is significantly below the diffusion-controlled limit. The slow decay of this radical is attributed to polar effects.