The equilibrium of the reaction: 2,4,6-tri-tert-butylphenoxyl radical (1)+2,6-di-tert-butyl-4-methyl phenol (2) --> 2,4,6-tri-tert-butylphenol (3) + 2,6-di-tert-butyl-4-methylphenoxyl radical (4) was studied from 243 to 298 K, for solutions 0.25 mol l(-1) in phenols, in two groups of experiments. In the first group the equilibria were obtained in benzene-toluene (1: 1) what yielded a second degree correlation in T-1: In K-eq = -23.31 + 1.3281 x 10(4) T-1 - 1.69038 x 10(6) T-2. In the second group the equilibria were performed in 0.25 mol l(-1) 1,4-dioxane solution in benzene-toluene (1:1) which gave a linear correlation: ln K-eq = 0.949 + 5.278 x 10(2) T-1, from which DeltaH(1) = 2.14 +/- 0.1 and D-sln (O-H) = 338.0 +/- 0.5 kJ mol(-1) in 2 were derived. The hydrogen bond of phenols to dioxane could explain the differences between the results found for the two sets of experiments.