Growth processes of the (0 1 1) and (0 (1) over bar 1) faces of an orthorhombic lysozyme crystal were observed in situ under 0.1 and 100 MPa, The growth rates of the (0 1 1) and (0 (1) over bar 1) faces were equal within an experimental error. From the comparison between the growth rates under 0.1 and 100 MPa at the same supersaturation level, we. found that the growth kinetics of the orthorhombic lysozyme crystals significantly decreases with an increase in pressure. Supersaturation dependencies of the growth rates under 0.1 and 100MPa were well fitted with a two-dimensional (2D) nucleation growth model of a birth-and-spread type. The fitting results show that the decrease in the growth kinetics with pressure can be explained by the increase activation energies in the incorporation processes of solute molecules. (C) 2003 Elsevier Science B.V. All rights reserved.