The assignments of the hydroxyl, hydroperoxyl, and alkylperoxyl radical spin adducts of α-phenyl N-tert-butyl nitrone (PBN) are discussed. Results of new experiments designed to test the assignments of the first two are described. It is concluded that the hydroxy adduct assignment is correct. The relationship between aβH and aN is[Formula: see text]This equation gives a good fit for the seven pairs of constants reported for the hydroxy adduct. The assignments for the hydroperoxy adduct may be correct but no proof is yet available for this assignment.