Chemical analyses revealed that polycyclic aromatic hydrocarbons (PAH's) and other organic compounds were present in a perennial freshwater stream that flowed through the abandoned American Creosote Works, designated for Superfund cleanup by the U.S. Environmental Protection Agency. A study was conducted to determine efficacy of ultrafiltration for removal of these organics from groundwater at the Superfund site. Ultrafiltration reduced the concentration of total identified organics from 210.0 mg/L in groundwater to 1.5 mg/L in the post-filtration permeate. Tests for toxicity/teratogenicity in embryonic inland silversides, Menidia beryllina; and Microtox were conducted with: streamwater, untreated groundwater, feedwater used in the ultrafiltration system and permeate water that passed through the ultrafiltration system. A concentration of 100% streamwater caused significant (alpha < or = 0.05) teratogenic responses in fish embryos and larvae. Groundwater and feedwater caused significant embryo toxic or teratogenic responses at concentrations of 100, 10 and 1%; Microtox EC50's were 0.85 and 0.48%, respectively. In contrast, only 100% permeate water caused significant increases in terata.