An Evans & Sutherland PS300 computer graphics system will be purchased and maintained for an initial three-year period. In addition, the package to upgrade the system to a PS340, with the capacity to model solid surfaces such as enzyme active sites and virus surfaces, will be purchased, as well as a conventional terminal to allow maximum efficiency in using the graphics terminal. The system will be used in the research programs listed above, for building newly determined protein and nucleic acid models, for building possible models of proteins based on known structures of similar proteins, for the design of drugs and the study of drug binding sites, and for the interpretation of X-ray diffraction and nuclear magnetic resonance data from a variety of molecules, ranging from oligopeptide antibodies to viruses. Most of the major users are already using instruments of this type through collaborative arrangements with other institutions, but only at a high cost in time and travel. The system will also be used by a large group of other users needing occasional use of a molecular modeling facility, in most cases for the study of interactions between proteins and small molecules.