Background: Many vascular effects of estrogens were cited, dependent on species and types of experiments, but the major effect is vasodilatiotion. Objectives: We studied the NO production in HUVEC cultures after incubation with 17alpha-estradiol and progesteron. Matherial and method. We used three groups of HUVEC: group I, in which we measured the basal production of NO; group II, in which we measured the NO production after incubation with 17alpha-estradiol 10^­5M for 30 min, group III, in which we measured NO production after incubation with 10^­5 Mprogesteron for 30 min. NO production was measured usingflowcytometry. Results: In group I the percent of NO producing HUVEC was 22± 0,81%; in group II, the percent increased to 37,7 ± 1,7%(p<0,05), and in group III to 30,7 ± 0,9% (p<0,05), respectively. Conclusions: By increasing the endothelial production of NO,estrogens and progesteron may be vasoprotective and areinvolved in young female vascular disorders.