Summary Introduction: Recently much attention has been focused on endothelin-1 (ET-1) and endothelin-1 converting enzyme (ECE-1) gene polymorphisms and connected changes in ET-1 concentration. Additionally, these processes have been shown to be possibly involved in preeclampsia susceptibility. The aim of this study was to evaluate the correlation between ET-1 (Lys198Asn) and ECE-1 (Thr341Ile) gene polymorphisms and the risk of gestational hypertension and preeclampsia. Material and methods: The study group consisted of 110 hypertensive (69 with gestational hypertension and 41 preeclamptic) pregnant women. The control group included 150 healthy pregnant women. The frequency of investigated polymorphisms was examined by polymerase chain reaction and restriction fragment length polymorphism (PCR/RFLP) assay. Results: There were no statistically significant differences in genotype frequencies of ET-1 Lys198Asn and ECE-1 Thr341Ile gene polymorphic variants between hypertensive pregnant women and the control group. There were also no remarkable differences between GH and PE groups when compared to the controls. However, parallel presence of both Thr341Ile ECE-1 and Lys198Asn ET-1 variant localisation showed a higher occurrence rate of ECE-1 CT/ET-1 GT heterozygotic genotypes in the control group (5,3%) than in the whole study or GH and PE groups (0.9%, 1.4% and 0.0% respectively, p=ns). In preeclamptic women, the higher systolic blood pressure value was observed in GG Lys198Asn ET-1 genotype carriers (180.7 mmHg) than in patients with at least one mutated T allele (GT and TT) (167.3 mmHg, p=ns). The lowest blood pressure level was connected with the mutated TT Lys198Asn ET-1 genotype presence. Conclusions: Results of this study suggest lack of direct correlation of Lys198Asn ET-1 and Thr341Ile ECE-1 gene polymorphisms with risk of gestational hypertension and preeclampsia in the studied population of Polish women. High prevalence of ECE-1 CT/ET-1 GT heterozygote genotypes of both Thr341Ile ECE-1 and Lys198Asn ET-1 polymorphisms in healthy pregnant subjects compared to GH and PE groups suggests the protective role of mutated alleles in the development of PE. The carrier of mutated TT genotype of Lys198Asn ET-1 polymorphism is probably connected with lower systolic blood pressure level in preeclamptic women. Future studies are needed to establish the role of analysed polymorphisms in the etiology of gestational hypertension and preeclampsia.