A mixed molecular dynamics/Monte Carlo (MD/MC) algorithm for constant pressure simulations of arbitrary molecular systems is examined. Calculations are reported at ambient and high pressures both for liquid water systems and for a chemical reaction step in a solvated enzyme utilizing empirical valence bond potentials. The present method reproduces earlier reported results well and is computationally efficient since it does not require the virial to be evaluated at each MD step. It is also found that the effects of introducing MC volume steps on the dynamics of the system are negligible provided that the volume step sizes and updating frequencies are appropriately chosen. (C) 2003 Elsevier B.V. All rights reserved.