A study of the toxicity of 150-ton R-17 oil shale process water to aquatic organisms is in progress. This water was generated during a simulated in situ retort experiment conducted with a reference western oil shale. Results of this study will, therefore, be appropriate for inclusion in the Department of Energy reference oil shale data base. The toxic effects of untreated, treated, and fractionated 150-ton R-17 process water were determined using bacteria (Microtox assay), zooplankton (Ceriodaphnia affinis/dubia), and fish (fathead minnow). A concentration of less than 1% process water was acutely toxic to all organisms tested. The toxicity of the water to the Microtox organism was substantially reduced following a treatment sequence of hot-gas stripping plus activated carbon adsorption plus reverse osmosis. Concentrations of less than 10% treated water were lethal to Ceriodaphnia and fathead minnows. Tests of the major fractions of 150-ton R-17 process water indicated that the organophilic fraction was more toxic to the Microtox organism while the hydrophilic fraction was more toxic to Ceriodaphnia and fathead minnows. Identification of the toxic constituents of 150-ton R-17 process water will be completed during the final stage of this study. 10 refs., 8 tabs.