Relative reactivities of C-H bonds in alkylbenzenes in the hydrogen abstraction by methyl radicals at about 950 K were determined by means of labeled compounds. The following values normalized to the primary aliphatic C-H bond were obtained : r(Ph-H) = 0.7 +/- 0.1; r(Bz-H) = 4.6 +/- 0.5; r(sec,benzyl) = 8.7 +/- 1.0; r(tert,benzyl) = 9.0 +/- 1.0. The combination of these high-temperature values with low-temperature kinetic data from the literature reveals the absence of a straight connection between strength and reactivity of C-H bonds.