The addition of several photochemically generated organic radicals (H-., CH3., C6H5., CF3. , and C2F5.) to ellipsoidal C-70 was studied by electron spin resonance. Three of the five possible isomers of RC(70)(.) were detected with R = H, CH3 and four with R = C6H5, CF3, C2F5. Arguments based on relative abundances and on comparisons of hyperfine interactions and g factors of the RC(70)(.) isomers and of their C-60 analogs allowed to place the isomers in homologous series and to identify the sites of radical addition on the C-70 surface leading to each isomer.