Ab initio calculations of adiabatic barriers for the prototypical radical hydrogen transfer (RHT) reaction, bimolecular transfer of hydrogen atom from ethyl radical to ethylene and, for comparison, the hydrogen abstraction reaction, ethyl + ethane, were carried out at the spin-projected UHF mp2/6-31g** level with thermal corrections. The mp2/6-31g** barrier for the abstraction reaction, 15.5 kcal/mol (vs experiment, 12.6 kcal/mol), can be compared with the much higher intrinsic barrier for RHT from ethyl to ethylene, 27.2 kcal/mol. The RHT barrier is less than that of hydrogen atom loss, 37 kcal/mol. This barrier, together with other considerations, suggests that the RHT reaction is a much higher energy pathway than widely assumed.