The reactions of tert-butoxyl radicals, generated by the pyrolysis of di-tert-butyl peroxide with cyclohexane and a number of methyl-substituted cyclohexanes have been studied. The Arrhenius parameters corresponding to overall hydrogen abstraction have been determined in the temperature range 399–434 K based on the values of the Arrhenius parameters for pressure-dependent decomposition of tert-butoxyl radicals obtained by Batt and Robinson (L. Batt and G. N. Robinson, Int. J. Chem. Kinet., 1982, 14, 1053). The compounds studied were cyclohexane, methylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,1-dimethylcyclohexane, 1,1,3-trimethylcyclohexane and 1,2,4-trimethylcyclohexane. Arrhenius parameters for the abstraction of secondary and tertiary hydrogen atoms by tert-butoxyl radicals have been determined to be log(A/dm3 mol–1 s–1)= 9.23 ± 0.07, E/kJ mol–1= 25.4 ± 0.9 and log(A/dm3 mol–1 s–1)= 9.90 ± 0.11, E/kJ mol–1= 22.2 ± 1.1, respectively.