The eight unique Diels-Alder cycloadditions of butadiene to C-70 are analyzed theoretically and compared with the well-established, two possible Diels-Alder cycloadditions of butadiene to C-60. Full geometry optimizations of reactants, adducts, and transition states are performed using the AM1 semiempirical method followed by single-point ab initio energy calculations. The results show that the cycloaddition of butadiene to the C-70 fullerene in the gas phase is slightly more reactive than that to C-60. However, in toluene solution calculations yield that the different solvent effects on C-60 and C-70 cause a significant decrease of the energy barrier in the C-60 cycloaddition, thus predicting a larger reactivity for C-60 as compared to the C-70 fullerene.