The crystallization of glycine and I-phenylalanine from water-isooctane microemulsions stabilized by AOT (sodium di-2-ethylhexyl sulfosuccinate) has been investigated. Crystallization phenomena were strongly affected by the localization of the solubilized molecules within the microemulsion droplets. In the case of glycine, which is solubilized within the water pools, a significant reduction in crystal size was observed in the temperature range investigated (T-i = 35 degreesC, T-c = 5 degreesC). While crystals formed in aqueous solution usually grow to millimeter sizes, glycine crystals grown from;microemulsions were submicron to micron in size. In addition, the alpha -form was only observed from aqueous solution, while the gamma -form was the predominant form from microemulsions. In the case of phenylalanine molecules, which are located primarily at the W/O interface, morphology and polymorphism were also affected in addition to crystal size. While phenylalanine crystallizes from aqueous solution in the form of two polymorphs, i.e., the needlelike alpha -form and platelike beta -form, upon crystallization from microemulsions, only the beta -form appeared. The different crystallization mechanisms of the two amino acids are discussed.