Three variants of murine serotonin transporter (5-HTT) mRNA, which consist of a different exon-one (exon 1a, exon 1b or exon 1c) and the same exon-two to exon-five, were identified. The promoter region for each exon 1 (p1a, p1b and p1c, respectively), ligated to pGL-3 enhancer vector, had activities significantly higher than the empty vector in all cell lines tested except p1c in PC-12, whereas the activity of p1c was significantly lower than the others. Effects of the treatment of dibutyryl-cyclic AMP, human interferon-alpha or mouse interferon-gamma have different profiles among COS-7, PC-12, C6 glioma and immortalized rat serotonergic raphe neurons, RN46A. These three promoter regions may play a role in the transcription of the 5-HTT and could offer a model of the regulation of 5-HTT production in humans and further the pathogenesis of depression.