We propose a new generalized-ensemble molecular dynamics simulation algorithm, which we refer to as the multibaric-multithermal molecular dynamics. This is the molecular dynamics version of the recently proposed multibaric-multithermal Monte Carlo method. The multibaric-multithermal simulations perform random walks widely both in the potential-energy space and in the volume space. From only one simulation run, therefore, one can calculate isobaric-isothermal-ensemble averages in wide ranges of temperature and pressure. We test the effectiveness of this algorithm by applying it to a Lennard-Jones 12-6 potential system. (C) 2004 Elsevier B.V. All rights reserved.