Method 8140 Organophosphorous Pesticides Parameters, of SW-846 was validated for use in the determination of 27 analytes in a single laboratory study. The method can be used for the analysis of 26 organophosphorous parameters in water, soil, and hazardous waste; the method is not suitable for monocrotophos because it showed poor recovery from soil and water. The performance of several GC columns, both packed and capillary, was established for the analysis of organophosphates. The use of megabore capillary GC columns over the use of packed columns specified in the current method is recommended for multiresidue organophosphorous analysis. Two phosphorus specific detectors, the flame photometric (FPD) and nitrogen phosphorus (NPD), were compared in terms of linearity, specificity, and sensitivity. Sample preparation and analysis techniques for organophosphates in aqueous and solid matrices were tested for ruggedness in order to identify critical method parameters. A proposed modification of Method 8140 is included together with accuracy and precision data for the determination of 26 method analytes in soil and water samples. Limited recovery data is also provided for additional organophosphorous compounds amenable to the method.