A simultaneous determination of 20 antidepressant drugs (imipramine, amitriptyline, desipramine, trimipramine, nortriptyline, clomipramine, amoxapine, lofepramine, dosulepin, maprotiline, mianserin, setiptiline, trazodone, fluvoxamine, paroxetine, milnacipran, sulpiride, tandspirone, methylphenidate and melitracen) in human plasma was developed using LC/MS with sonic spray ionization (SSI) method. These drugs showed good separation and sensitivity by LC-MS using an Inertsil C-8 column with methanol:10mM ammonium acetate (pH 5.0):acetonitrile (70:20:10) as mobile phase at 0.10 mL/min at 35 degrees C. Solid-phase extraction of these drugs added to the human plasma was performed with an Oasis HLB cartridge column. Recovery and limit of detection of these drugs were between 69 and 102% and between 0.03 and 0.63 microg/mL, respectively. The present procedure offers an easier and more convenient screening method for antidepressants, and will be useful for forensic toxicology investigations.