Recent advances in protein crystallography have significantly shortened the time and labor required to determine the three-dimensional structures of macromolecules once good crystals are available. Crystal growth has become a major bottleneck in further development of protein crystallography. Proteins and other biological macromolecules are notoriously difficult to crystallize. Even when usable crystals are obtained, the crystals of essentially all proteins and other biological macromolecules are poorly ordered, and diffract to resolutions considerably lower than that available for most crystals of simple organic and inorganic compounds. One promising area of research which is receiving widespread attention is protein crystal growth in the microgravity environment of space. A series of protein crystal growth experiments were performed on US shuttle flight STS-26 in September 1988 and STS-29 in March 1989. These proteins had been studied extensively in crystal growth experiments on earth prior to the microgravity experiments. For those proteins which produced crystals of adequate size, three-dimensional intensity data sets with electronic area detector systems were collected. Comparisons of the microgravity-grown crystals with the best earth-grown crystals obtained in numerous experiments demostrate that the microgravity-grown crystals of these proteins are larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions. Analyses of the three-dimensional data sets by relative-Wilson plots indicate that the space-grown crystals are more highly ordered at the molecular level than their earth-grown counterparts.