Ten analytes from the U.S. Environmental Protection Agency's SW-846, Method 8140, Organophosphorous Pesticide Parameters, were subjected to analysis by high performance liquid chromatography/mass spectrometry (HPLC/MS) and HPLC/MS/MS with thermospray ionization. The compounds chosen suffered poor recoveries under analysis by Method 8140 which is a gas chromatographic procedure. Limits of detection, precision values, and retention times were generated with HPLC/MS methods on pure analytical standards. Collision activated dissociation daughter ion spectra were also collected by tandem mass spectrometric techniques. Four environmental samples known to contain organophosphorous pesticides were analyzed by HPLC/MS, and these results were compared with similar analyses by GC/MS. Tandem mass spectrometry was used to confirm the compounds identified by HPLC/MS.