Background and objective: Serotonin plays an important role in the pathophysiology of aggressive behavior. Low serotonin levels and altered functions of serotonin receptors affect suicidal behavior. TPH-1, TPH-2 and SLC6A4 genes have important roles in serotonin production and degradation pathways. In this study, polymorphic variants of the TPH-1, TPH-2 and SLC6A4 genes, rs1800532, rs7305115, rs6355 and rs1386494, were investigated in 100 completed suicides and 100 healthy individuals. Materials and methods: After DNA isolation, a new polymerase chain reaction technology KASP TM (Competitive allele-specific polymerase chain reaction method), was used in the genotyping of the selected gene variants. Results: No statistically significant difference was found for the genotype and individual allele frequencies of the polymorphic variants between suicide and control groups, as well as between men and women in suicide cases. However, we observed non-significant tendencies of increased minor alleles in suicidal men for all TPH SNPs. Conclusions: More molecular genetic research studies are needed to understand the pathophysiology of suicide and to reveal its relationship with gender.