B3LYP BDEs by Moore et al. and BMK BDEs calculated in this work agree moderately (R 2 = 0.851, MAD = 14.3 kJ/mol, ??), but better if BMK BDEs of model peptides with smaller capping groups are used (R 2 = 0.910, MAD = 12.6 kJ/mol, ??). The difference between the BDEs at the two levels of theory is particularly pronounced for C α -H BDEs. The poor performance of B3LYP becomes most noticeable if compared to the G4(MP2)-6X results (MAD = 10.6 kJ/mol, ??). The linear fit shows a reasonable R 2 = 0.933, but a slope of 0.775 and an intercept of 86.4 kJ/mol. For low BDEs, such as for C α -H bonds and C-H bonds adjacent to O or S atoms, B3LYP values are too low. For higher BDEs, such as for O-H and secondary C-H bonds, B3LYP values are too high. The B3LYP BDE for the cysteine S-H bond is also much larger than at the G4(MP2)-6X level of theory.