A multiresidue isolation technique known as matrix solid-phase dispersion (MSPD) is presented for the extraction and subsequent gas chromatographic/electron capture detection (GC/ECD) determination of 14 chlorinated pesticides (alpha-BHC, beta-BHC, lindane, heptachlor, aldrin, heptachlor epoxide, p,p'-DDE, dieldrin, endrin, 4,4'-DDD, endrin aldehyde, p,p'-DDT, endosulfan sulfate, and methoxychlor) from oysters (Crassostrea virginica). Pureed whole oysters (0.5 g aliquots) are fortified with the 14 pesticides and delta-BHC, as an internal standard, and blended with 2 g C18 (octadecylsilyl)-derivatized silica. Pesticides are eluted from an extraction column composed of C18/oyster matrix blend and 2 g activated Florisil by addition of 8 mL acetonitrile-methanol (90 + 10). Then, 2 microL of the eluate is analyzed by GC/ECD. Unfortified blank controls are treated similarly. The eluate contained all the pesticide analytes and was free of interfering coextractants. Correlation coefficients for the standard curves of the 14 extracted pesticides (linear regression analysis) ranged from 0.9849 to 0.9980. Average relative percent recoveries over the range of concentrations examined (66 +/- 12.7% to 84 +/- 25.3%, n = 25 for each pesticide), interassay variability (13.6 +/- 8.8% to 30.2 +/- 9.1%, n = 25 for each pesticide), and intra-assay variability (5.8-11.8%, n = 5 for each pesticide) indicated that the MSPD methodology successfully extracted and determined the 14 chlorinated pesticides in oyster at levels of 31.3-500 ng/g.