This paper describes the solid-phase extraction (SPE) Twin-PA1 large volumeinjection (LVI)-gas chromatography (GC) technique which has been effectivelyused in the online in-situ analysis of semi-volatile organic compounds in drinking water. Linear calibrations over a concentration range of 0.05 to 5.0 ug/L have been obtained for most pesticides included in this study. Method detection limits were below 0.1 ug/L. Recoveries at a range of 70-130% and percent relative standard deviations of less than 10% have been obtained for most pesticides studied in the analysis of reagent water and tap water.These results indicate that this new technology has several obvious advantages over other SPE-GC-MS methods for the analysis of semi-volatile organic compounds in aqueous samples. Includes 28 references, tables.