A versatile free-radical trapping agent, 1,1,3,3-tetramethylisoindolin-2-yloxyl, has been prepared from N-benzylphthalimide by reaction with 'methylmagnesium iodide' in refluxing toluene followed by hydrogenolysis and oxidation. The Grignard reaction gives 2-benzyl-1,1,3,3-tetramethylisoindoline along with a small proportion of an unexpected by-product, 2-benzyl-1-ethyl-1,3,3-trimethyliso-indoline.