Crystals of the enzyme RNase S were grown at micro and unit gravity using a dialysis-based dynamically controlled device. Crystals were grown at 24degreesC on space shuttle flights STS 93 and STS 95. Control crystals were grown simultaneously in ground laboratories using identical equipment. Sizes, shapes, populations, and diffraction resolution have been compared and the crystals analyzed by X-ray topography. The sizes, populations, and resolutions of the two classes of crystals were not significantly different. The shapes of the space-grown crystals were more complete and symmetric, consistent with their unattached growth (ground crystals generally grow on the dialysis membrane). The two sets of crystals have distinct topographic signatures consistent with different growth dynamics. Topographs of microgravity grown crystals share a pattern with relatively higher symmetry and higher intensity. This is probably due to the symmetric growth environment of their microgravity growth. The structure of the space topographs suggests a time and symmetry dependent growth process that is probably disrupted by gravity-induced, asymmetric effects,in earth grown crystals. (C) 2003 Elsevier Science B.V. All rights reserved.