Constant pressure and temperature molecular dynamics techniques have been employed to investigate the structure of two unit cells of a hydrated bovine trypsin inhibitor type I crystal at T = 300 K and P = 0.1 MPa. The simulations carried out with two different force fields and including full long-range electrostatics showed small deviations from the experimental structural results. This confirms previous calculations done at constant volume on a smaller sample. Our simulations have also shown differences in the water diffusion results obtained for the two force fields.