Protein crystal growth experiments have been performed on 16 space shuttle missions since April 1985. The initial experiments used vapor diffusion crystallization techniques similar to those used in laboratories for earth-based experiments. More recent experiments have assessed temperature-induced crystallization as an alternative method for growing high quality protein crystals in microgravity. Results from both vapor-diffusion and temperature-induced crystallization experiments indicate that protein crystals grown in microgravity may be larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth. © 1994.