Rate coefficients for the reactions of hydroxyl (OH) and nitrate (NO3) radicals with the six dirnethylphenols have been determined at 295 +/-2 K and atmospheric pressure using the relative rate technique. Experiments were performed in a 3.91 m(3) atmospheric simulation chamber using in situ FTIR spectroscopy and gas chromatography for chemical analysis. The reactivity of the dimethylphenols is compared to other phenolic compounds and it is shown that the rate coefficients strongly depend on the number and position of the OH and CH3 substituents around the aromatic ring. In addition, the dimethyl phenol isomers appear to exhibit an opposite trend in reactivity for reaction with OH and NO3 radicals. The rate coefficient data for the dirnethylphenols and related phenolic compounds are explained in terms of known mechanistic features of the reactions. The atmospheric implications are also discussed.