The removal of over 40 toxic compounds, including heavy metals, synthetic pesticides and organic compounds, by cellulose acetate (CA) and crosslinked-polyethylenimine (C-PEI) membranes were examined. With few exceptions both membranes removed 97+ percent of the heavy metals and pesticides tested; the C-PEI membrane was found to be somewhat more effective than the CA membrane. In addition, the C-PEI membrane removed 70+ percent of 13 of the 19 organic compounds tested; only two compounds were removed less than 50 percent. In contrast, however, the CA membrane removed less than 50 percent of 16 of the 19 organic compounds tested, and three compounds were found to exhibit negative removal. The ability of C-PEI membrane to remove organic compounds and its resistance to high temperature and pH have made reverse osmosis an effective separation process for the removal of toxic compounds from water.