The potential of supercritical fluid technology for water analysis has been recognized for nearly a decade. In an effort to broaden the knowledge required to implement methods for the direct extraction of water samples, we have investigated the partitioning of chlorinated, acidic pesticides and phenols between mater and carbon dioxide. A high-pressure stainless steel extraction vessel with on-line HPLC detection was constructed for solubility and partitioning experiments. The solubility of pentachlorophenol in both water and liquid CO2 was determined at ambient temperatures as a function of pressure. A solubility isotherm was also constructed at 28.1 degrees C for CO2. Solubility isotherms of 2,4-dichlorophenoxyacetic acid in liquid and supercritical (SC) CO2 have been measured at (21.0, 26.3, and 34.8) degrees C. Naphthalene solubility in SC CO2 was measured at 34.7 degrees C and compared with literature values to ensure correct function of the apparatus. Measurements were performed at pressures up to 250 bar.