Fractional precipitation is a simple, efficient method for pre-purifying paclitaxel from plant cell cultures. The storage temperature of fractional precipitation was optimized in terms of the yield and purity of paclitaxel with a fixed methanol concentration in water (61.5%, v/v), paclitaxel content in the crude extract (0.5%, w/v), and storage time (3 days). The greatest yield (similar to 84%) was obtained with storage at a constant temperature (0 degrees C) for 3 days. Conversely, the highest purity (similar to 79%) was obtained with stepwise reduction in temperature over 3 days. For a constant storage temperature, the maximum purity (similar to 67%) was obtained at 0 degrees C. There was little difference in the yield of paclitaxel between -20 and 12 degrees C. At a constant storage temperature (0 degrees C), both the precipitate yield and purity increased rapidly up to 18 h, and then increased more slowly. This pre-purification process serves to minimize solvent usage, and the size and complexity of the high-performance liquid chromatography (HPLC) operation required for paclitaxel purification. (c) 2005 Elsevier Ltd. All rights reserved.