Quantitative determination by liquid chromatography (LC) coupled with mass spectrometry (MS) was achieved for the following 10 toxins found in association with diarrhetic shellfish poisoning: okadaic acid (OA), dinophysistoxin-1 (DTX1), 7- O-palmitoylokadaic acid (palOA), 7- O-palmitoyldinophysistoxin-1 (palDTX1), pectenotoxin-1 (PTX1), pectenotoxin-2 (PTX2), pectenotoxin-2 seco acid (PTX2SA), pectenotoxin-6 (PTX6), yessotoxin (YTX), and 45-hydroxyyessotoxin (YTXOH). Toxins in 2 g of the adductor muscle or the digestive glands of scallops, Patinopecten yessoensis, were extracted with 18 ml of methanol–water (9:1, v/v), freed of polar contaminants by partition between chloroform and water, and treated by solid-phase extraction on a silica cartridge column. Samples containing YTXOH were purified separately on a buffered reversed-phase column. Chromatographic separation was achieved by the following combinations of columns and mobile phases: a Symmetry C 18 column with acetonitrile–0.05% acetic acid (7:3, v/v) for OA, DTX1, PTX6 and PTX2SA; a Develosil ODS column with the same mobile phase for PTX1 and PTX2; a Capcellpak column with methanol–2.5% acetic acid (98:2, v/v) for palOA and palDTX1; and an Inertsil ODS column with methanol–0.2 M ammonium acetate (8:2, v/v) for YTX and YTXOH. Carboxylic acid toxins were selectively monitored on [M−H] − ions, sulfated toxins on [M−Na] − ions, and neutral toxins on [M+NH 4] + ions. Average recoveries of the toxins spiked to tissue homogenates ranged from 70 to 134%. Detection limits in the muscle ranged from 5 to 40 ng/g and those in the digestive glands from 10 to 80 ng/g.