The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C-70 was Studied by electron spin resonance and the results were compared with those obtained with C-60. While simple alkyl radicals afford only three of the five expected RC(70)(.) regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC60. and for the five HC70. regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC(70)(.) regioisomers.