The range of chem. problems that are directly accessible to first-principles mol. dynamics simulations based on d. functional theory is extended with a novel method apt to accelerate rare reactive events. The introduction of a finite electronic temp. within the Mermin formalism leads to a lowering of chem. activation barriers and thus to an exponential enhancement of the rate at which these reactions are obsd. during a first-principles mol. dynamics simulation. The method presented here makes direct use of the intrinsic chem. information encoded in the electronic structure, and is therefore able to lower selectively chem. relevant activation energies even in systems where many competing low-energy pathways for conformational transitions or diffusive motions are present. The performance of this new approach is demonstrated for a series of prototypical chem. reactions in gas and in condensed phase. A typical acceleration that can be achieved is, for example, a factor of 105 for the cis-trans isomerization of peroxynitrous acid in aq. soln. at room temp. [on SciFinder (R)]