Solubility equilibria of threonine in water/ethanol mixtures were measured in the temperature range between (10 and 46) degrees C. Threonine exhibits good solubility in water and is hardly soluble in ethanol. The ternary-phase diagram of the threonine enantiomers in the solvents used reveals the presence of a conglomerate-forming system. Threonine shows ideal solution behavior (i.e., heterochiral interactions do not occur in solution). To correlate the measured data with regard to temperature and solvent composition, a simple empirical approach is proposed. The correlation presented is of interest for calculation of solubilities when designing crystallization or chromatography-based processes to separate the threonine enantiomers.