The CVT growth of ZnSe single crystals under micro-gravity (mug)-conditions was investigated in comparison with the corresponding ground-based (1g) experiments. The transport rates have been found to be considerably higher than the computed values accounting mainly for diffusion and Stefan flow. Different types of convection may be masked or superimposed by thermal convection when under 1g-conditions. The quality of mug-grown crystals was improved even at such high mass transport rates that arise at 1g-experiments. (C) 2002 Elsevier Science B.V. All rights reserved.