The project is designed to develop new instrumentation and methods (or to improve existing ones) for characterization of biological macromolecules and for study of their interactions. Analytical ultracentrifugation, the techniques ancillary to it, and methods of data analysis using mathematical modeling appropriate for these techniques are the major areas of interest. Major emphasis in this project has been given to applications of mathematical modeling to problems in ultracentrifugal analysis. This principal of concern has been to extend the method of implicit constraints to a wider range of studies of macromolecular interactions and in particular analyzing combined homogeneous and heterogeneous associations. MLAB software, operating on the DEC-10 computer, has been used for the mathematical modeling. The applications of these studies are described in the project report 10184-04, Physical Chemistry of Biological Macromolecules. A feasibility study continues toward development of a low-cost optical data acquisition system (based upon fluorescence scanning) that would convert existing preparative ultracentrifuges into analytical ultracentrifuges.