Serotonin-induced neuronal cell death has been implicated as a possible cause of neurodegenerative and neuropsychiatric disorders. To investigate the involvement of serotonin-induced apoptosis as a potential mechanism in the pathophysiology of serotonin-related diseases, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, DAPI (4',6-diamidino-2-phenylindole) staining, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) assay and flow cytometric analysis were performed using the immortalized pineal cell line PGT-beta. Through morphological and biochemical analyses, it was demonstrated that cell death induced by serotonin in PGT-beta cells shows classic apoptotic features. These data suggest that serotonin induces apoptosis in PGT-beta cells.