An algorithm for the calculation of reaction paths between known reactant and product states in systems of low or high dimension is described, The optimal reaction path is defined as the path of maximum Aux for a diffusive dynamics assuming isotropic friction. The resulting reaction path is temperature dependent and independent of the magnitude of the friction, Comparison is made with a number of algorithms designed for the calculation of minimum-energy reaction paths. Applications to two model potentials and an extended atom model of a dipeptide are presented. The applications demonstrate the ability of the algorithm to isolate a temperature-dependent optimal reaction path for a high dimensional molecular system. (C) 1997 American Institute of Physics.