Methodology was developed for the isolation and recovery of ompounds from a commercial lampricide formulation associated with hepatic mixed function oxygenase (MFO) enzyme induction in fish. MFO induction in laboratory bioassays was characterized and optimized prior to fractionation experiments. Recovery and isolation of MFO activity directed the chemical fractionations. Fractionation techniques were developed on a preparative scale so that fish exposures could be conducted directly. Formulation impurities associated with MFO induction were separated from the active lampricide using solid phase extraction. Subsequent HPLC fractionations isolated activity in distinct fractions, indicating that multiple formulation impurities are associated with the observed MFO induction. Activity was recovered from each fraction using toluene extraction and the extracts werecharacterized by GC-MS. No activity was associated with several compounds confirmed in the bioactive fractions and other structures are proposed. A preliminary application of these techniques to potential reproductive dysfunctions in fish is discussed.