Antidepressants belong to a variety of chemical and pharmacologic classes. Most require therapeutic drug monitoring, at least in certain circumstances, such as unexplained inefficacy or suspected toxicity. Several types of chromatographic methods have generally been used. This paper presents a fully automated, sensitive, and specific method for the therapeutic drug monitoring of 13 antidepressants of all classes (amoxapine, amitriptyline, citalopram, clomipramine, dothiepin, doxepin, fluoxetine, imipramine, maprotiline, mianserin, paroxetine, sertraline, trimipramine) and some of their respective active metabolites (nortriptyline, monodesmethylcitalopram, desmethylclomipramine, desipramine, norfluoxetine, desmethylmianserin, N-desmethylsertraline), based on the innovative turbulent-flow liquid chromatography (TFC) technology, coupled to tandem-mass spectrometry (MS/MS). The antidepressants were divided in two groups depending on their chromatographic properties, so that two injections would be necessary to screen all compounds (which is infrequent for therapeutic drug monitoring). Calibration curves ranged from 10 to 500 ng/mL. No significant memory effect was observed after the injection of a blank serum sample spiked at 500 ng/mL. The intra-assay and inter-assay precision CVs ranged from 0.4% to 12% and from 1% to 16%, respectively. The method was further validated by blindly analyzing Heathcontrol-Therapeutic Drugs Scheme samples (Cardiff Bioanalytical Services Ltd.) containing several antidepressants.