The EPR spectrum of 6-oxy-benzo[alpyrene (6-oxy-BaP) radical in CH 2Cl 2 has been reanalyzed in light of data obtained from 13C singly labeled 6-oxy-BaP radicals, in terms of 11 proton splitting constants, in gauss: 0.105, 0.270, 1.102, 1.135, 1.275, 1.415, 1.660, 4.460, 4.720, 4.803, and 5.603 (±0.005). Assignments have been made on the basis of the EPR data of monomethyl 6-oxy-BaP radicals and HMO calculations. The proton splitting constants found from an ENDOR spectrum of 6-CF 3CO 2-BaP (6-TFA-BaP) cation radical have also been assigned to specific positions by analogy with the methyl splittings of monomethyl 6-TFA-BaP radicals and HMO calculations. The assignments of proton splittings for both 6-oxy-BaP and 6-TFA-BaP are supported by the consistency of the 13C splitting data obtained under the same conditions from the 12 singly labeled 6-oxy-BaP and 6-TFA-BaP radicals.