Determination of conditions suitable for crystallizing macromolecules often involves many iterative trials. The current standard procedure of manual design of experiments (including manual calculation of volumes of reagents) and recording observations by hand, is tedious, susceptible to errors, makes organization of records and searches for patterns difficult, and is not suited to automation. We have therefore written Etray, an open-source program that is freely obtainable over the Web, Elkin, C., Hogle, J., http://sbweb.med.harvard.edu/similar to hogle/etray (2000), to automate record keeping, most aspects of experimental planning, and to facilitate computational analyses of these results. Etray displays an image of a standard 24 well crystal tray and allows the user to add reagents in appropriate concentrations to the wells, either individually or using tools for grid searches and incomplete factorial design. Etray automatically calculates volumes of stock solutions necessary to achieve the specified concentration, and contains tools for sketching, commenting and scoring the well contents. Speech recognition features allow the observations to be spoken out loud while the investigator looks into the microscope. An example of the use of Etray to design and analyze an incomplete factorial crystallization experiment is presented.