The focus of the proposed research is to find methods and procedures to improve the overall quality of x-ray diffraction results. X-ray diffraction crystallography remains one of the most powerful tools for determining the structure of molecules of all types, including compounds of biological interest; it can provide unambiguous and highly accurate description of molecular structures. However, with the advent of highly automated procedures for carrying out crystal-structure studies, a disturbingly large number of structures reported in the recent literature almost surely contain fundamental errors. The most common error seems to be that of describing the structure in a space group of unnecessarily low symmetry, which may lead to large errors in the atomic positions. We hope to arrive at routine procedures for avoiding these errors. We shall also investigate the effects of various experimental errors, such as misallignment of the crystal on the diffractometer and inappropriate absorption corrections. We shall continue our efforts to find a reliable technique for correcting for truncation errors normally encountered in measurements of high-angle reflections, which are very important in accurate studies of outer-shell electron density distributions. In sum, we shall concentrate on methods of increasing both the reliability and the accuracy of this very powerful technique for biochemical research.