The novel fast-growth or multiple steering mol. dynamics (MSMD) technique has been recently developed by Jarzynski to calc. free energy profiles along general transformation pathways (Phys. Rev. Lett. 1997, 78, 2690-2693; Phys. Rev. E 1997, 56, 5018-5035). Here, we apply this approach to calc. free energy barriers involved in the water exchange reaction of Na+ and K+ in aq. soln. We investigate the influence of the key parameters of the MSMD simulations-the steering velocity, the sampling of the initial configurations, and the force const.-on the free energy. Furthermore, we use this approach to describe energetical and structural features of the water exchange reaction of Na+ and K+ in aq. soln. The MSMD technique turns out to be an efficient and fast convergent tool to enhance the sampling of rare chem. events with the help of nonequil. forces. [on SciFinder (R)]