Direct numerical simulations have been carried out to examine the nature of g-jitter induced convective flows during a typical protein crystal growth experiment in a microgravity environment. The numerical investigations identified six parameters of importance for the motion of a spherical crystal particle in a microgravity environment subjected to single frequency vibrations in one direction: frequency (f) and amplitude (A) of the applied vibration, particle radius (R) and density (rho(p)), fluid density (rho(f)) and fluid viscosity (v). In the Stokes regime, the numerical results were found to be in good agreement with the analytical results of Coimbra and Rangel [AIAA J. 39(9)(2001)]. Beyond the Stokes regime (1 < Re-p < 300), the particle motion amplitude was found to approach the cell vibration amplitude to within 1% when the ratio a alpha(2)/S (alpha = rho(f)/rho(p), S = f R-2/9v) becomes greater than about 20. Most importantly, the present results show that the g-jitter-induced convective flows are likely to occur during the microgravity crystal growth on space platforms. In a typical protein crystal growth process involving a crystal of rho(p) = 1.2 g/cm(3) and 10-1000 mu m diameter in an aqueous solution, g-jitter-induced crystal motion and convection have been predicted to occur even at acceleration levels as low as 1.0 mu G. (c) 2006 Elsevier B.V. All rights reserved.