The proposed research relates to development of principles for engineering the crystallization product of organic electrolyte solutions. Models to describe adequately the nucleation and growth rates and to elucidate precipitation mechanisms of organic electrolytes have been proposed for experimental verification. Emphasis will be placed on developing heuristics for predicting the inclusion of the additives in the precipitate and the role of included additives on the properties of the precipitate crystals. The significance of this research is its relation to the design of solids with carefully engineered physicochemical and biological properties. These properties can dramatically affect the biological activity of pharmaceutical products. It is expected that the goals of the project will be accomplished by studying the precipitation kinetics of a monoprotic acid (diphenylhydantoin) and an amino acid (glutamic acid). The influence of other amino acids and other structurally related additives will be studied from both a structural and a kinetic points of view.