The SEDNTERP sedimentation interpretation/database program is a general purpose tool for the interpretation of sedimentation velocity and sedimentation equilibrium experiments. It collects many diverse functions into a single program. The program both uses a database of information about amino acids, common salts and buffers, etc., and allows the user to build a second database of information about samples, solvents, experimental results (sigma values from sedimentation equilibrium and raw sedimentation coefficients), and interpreted results (molecular weights, S20w, f/fo, axial ratios, etc.). The program requires Microsoft Windows (3.1 or Win95). Among the things SEDNTERP will do are: 1) Estimate solvent densities and viscosities for 93 salts and buffer components, using interpolation formulas based on data from the CRC Handbook of Chemistry & Physics and other sources. 2) Calculate protein molecular weights, partial specific volumes, and hydration based on amino acid composition. A long list of protein conjugates such as sugars, cofactors, and metal ions can also be added to the amino acid composition. Partial specific volumes can also be corrected for the presence of 8M urea or 6M guanidine hydrochloride. 3) Perform basic manipulations and reduction of raw sedimentation data: converting sedimentation coefficients to standard conditions, interconversion between buoyant and true molecular weight, and converting sigma values from sedimentation equilibrium to molecular weight. 4) Derive hydrodynamic parameters from sedimentation coefficients: frictional coefficients, minimum frictional coefficients, Stokes radius, maximum degree of hydration, and axial ratios for ellipsoid and cylinder models. All such calculations are done using both the "vbar" and "Teller" methods. Diagrams of the derived molecular shape and absolute size, and graphs of axial ratio versus hydration may be displayed and printed. 5) Sum amino acid sequences to derive the amino acid composition for use in vbar or sequence molecular weight calculations. Sequences can be cut and pasted from other sources such as sequence databases, or entered manually, and the sequence is stored in the database along with other information about that sample. 6) Calculate protein extinction coefficients, charge, and isoelectric points based on their composition. Graphs of charge versus pH (titration curves), and of predicted absorption spectra (250-320 nm) are also available. 7) Extend the physical constant databases with new information from the user. The user may add data for such things as non-natural amino acids, other protein conjugates, and densities or viscosities of other solvent components. 8) Store and retrieve information and results about the user's own sedimentation experiments. The user creates "sample" records defining a sample name, vbar, MW, and hydration, and named "buffer" records defining solvent density, viscosity, and pH. Then "experiment" records are created with experimental sedimentation coefficients and/or sigma values for a pair of "sample" and "buffer" records. Finally, "result" records can be created for a defined hydrodynamic analysis of a given "experiment" record, such as a prolate ellipsoid shape analysis using the Teller method. The SEDNTERP program grew out of the chapter "Computer-Aided Interpretation of Analytical Sedimentation Data for Proteins" by Tom Laue et al. in the Harding, Rowe, and Horton 1992 book, and it largely follows the terminology and computational methods outlined there. An extensive Windows Help file is available with the details of the methods and computations. The program code and Help file were originally developed by David Hayes in collaboration with Tom Laue. Over the last two years these were then extended and modified by John Philo at Amgen, resulting in the current released version. A small example database with a few defined samples and buffers is distributed along with the program to help illustrate its use.