The oxidation of a series of 4,4'-alkylidenebis(2,6-di-t-butylphenols) having increasing substitution of the central methylene carbon by alkyl groups is examined. In the monosubstituted compounds the stability of the monophenoxy radical increases with increase in the size of the substituent, while the stability of the galvinoxyl type radical decreases. ß-Coupled products are only obtained from the ethylidene bisphenol, a result that can be correlated with e.s.r. hyperfine splitting constants. With increasing mono- or di-substitution bisspiroperoxides become the preferred oxidation products. The e.s.r. spectrum of an ethylenebisgalvinoxyl biradical is described.