The extraction of phytochemicals from plants and their downstream processing is often associated with solvents, which are problematical with respect to health, safety, and environment. An alternative approach is the extraction with aqueous two-phase systems, which offers a benign environment for complex molecular structures. Particularly nonionic surfactants like, e. g., Genapol (R) X-080 and Tween (R) 65 in high concentrations in water can be used to form aqueous two-phase systems. Sage (Salvia triloba) is used as a model plant, since it contains a relatively high concentration of the two triterpenes oleanolic acid (OA) and ursolic acid (UA), which are interesting due to their wide range of biological effects. Kinetic experiments have shown that an extractive isolation of triterpene acids using such mesophase systems is possible.