Serotoninergic system is one of the major brain neurotransmitter systems that is involved in the development of depressive spectrum disorders. Regulatory genes of this system are the principle candidate genes predisposing to unipolar depression. Using PCR-RFLP analysis, we have conducted a study of polymorphic loci of several genes of this system: C1019G of serotonin receptor 1A gene, (HTR1A); A-1438G of serotonin receptor 2A gene, (HTR2A); G861C of serotonin receptor 1B gene, (HTR1B); Stin2VNTR and 5-HTTLPR of serotonin transporter gene (SLC6A4) in patients with unipolar depression from Tatar and Russian population. The results of the study suggest that genotype 10/10 of the SLC6A4 gene as well as genotype G/G and allele G of the HTR2A gene can predispose to increased risk of unipolar depression development in ethnic Russians. In contrast, genotype 12/10 of the SLC6A4 gene is a marker of low risk of the disease in both groups.