Haplotypes formed by polymorphisms (T-786C, rs2070744; a variable number of tandem repeats in intron 4, and Glu298Asp, rs1799983) of eNOS gene were associated previously with gestational hypertension (GH) and preeclampsia (PE). However, no study has explored the tagging SNPs rs743506 and rs7830 in these disorders.The aim of the current study was to compare the distribution of the genotypes and haplotypes formed by the two tagging SNPs or by the five eNOS polymorphisms mentioned among healthy pregnant GH and PE.We recruited 122 HP, 138 GH and 157 PE. Genotypes for the T-786C, the Glu298Asp and rs743506 polymorphisms were determined by Taqmanâ Allele Discrimination assays and fluorescence signals were measured on Chromo 4 Detector (Bio-Rad Laboratories, USA). Genotypes for the VNTR polymorphism in intron 4 and rs7830, however, were determined by PCR and fragment separation by electrophoresis in 8% polyacrylamide gels. Plasma aliquots were analyzed in triplicate for their nitrite content using an ozone-based chemiluminescence assay.The haplotype formed by the most common variants in each polymorphism "T b G A C" was more frequent in PE group compared to HP (P=0.00004), which may be explained by the higher linkage disequilibrium found in PE compared to GH and HP. Conversely, the haplotype "C b G G C" was more frequent in HP compared to PE (P=0.00113), which is supported by previous findings that demonstrated the association of the combination "C b G" with higher level of nitrite (NO marker).Our results suggest a protective effect of the haplotype "C b G G C" against the development of PE. This study was funded by the Fundação de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG-Brazil), the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP-Brazil).