The authors' recent studies on phenols and benzoic adds suggest that the ability of solid organic compounds to nucleate freezing of supercooled water may be predicted, at least in a limited number of cases, from purely thermodynamic considerations. A report that pure, optically active amino acids nucleate freezing at temperatures different from their inactive forms suggests that a quantitative study of the differences might be revealing. It was found that differences in nucleation temperature were related in a linear manner to differences in heat of solution of active and racemic forms. Tyrosine is an exception to the above behavior. It is suggested that nucleation on one of the forms may occur at the phenolic group.