Crystals of thaurnatin and of lysozyme from turkey and hen egg white have been prepared in batch at 20degreesC under hydrostatic pressures in the 0.1-220 MPa range. The latter model protein served as a reference in this comparative study. Crystallization was performed in an agarose gel in contrast to former studies under pressure that were conducted in solution. After depressurization, the habit, number, length, shape and solubility of crystals were compared to those of control crystals that were prepared at atmospheric pressure (0.1 MPa). For the three proteins, the number of the crystals increases with pressure. For thaurnatin and hen lysozyme, crystal length decreases but for turkey lysozyme it increases. While the solubility of the first protein decreases, that of both lysozymes increases. The relationship between solubility and pressure is linear in the three cases. The crystallization volumes DeltaV are -11cm(3)mol(-1) for thaumatin, +15cm(3)mol(-1) for turkey lysozyme and +3cm(3)mol(-1) for hen lysozyme. For the lysozymes, they are explained by pressure-dependent conformational changes. The structure of thaurnatin appears to be less deformable under pressure. (C) 2002 Elsevier Science B.V. All rights reserved.