The disclosure relates to methods for preparing urushiol from plants including, for example, poison ivy or poison oak. The methods include extraction of plant material using a primary organic solvent more polar than ethanol, followed by a solvent extraction using substantially immiscible solvents having substantially different polarities, such as hexane and acetonitrile. The method can include further purification, such as by fractionation of solvent-extracted materials using a thiazole-derivatized silica gel chromatography medium. The extracts thus generated can exhibit greater purity, higher concentration, and greater stability than extracts made using previously-known methods. The extracts can be particularly suitable for use in immunotherapeutic methods, such as desensitizing individuals who normally develop allergic contact dermatitis attributable to poison ivy or poison oak.