We examine the effect of the diagonal Born-Oppenheimer correction on dynamics in two simple systems - the Hooke's atom in an external harmonic potential and the collinear hydrogen exchange reaction. The transmission probability for the Hooke's atom, calculated within the Born-Oppenheimer approximation, is simply shifted in energy with respect to the exact result, and this is corrected by the diagonal adiabatic contribution. The reaction probability for the H-3 system reflects the fact, that the diagonal Born-Oppenheimer correction raises the barrier to the reaction by approximately 70 cm(-1).