Background: The aim of the study is to define the possibility of usage of the gene eNOS polymorphisms as molecular-genetic markers of athletes' resistance to exercise-induced hypoxia.Material/Methods: 127 highly qualified athletes were examined (30 persons are underwater finswimmers, 41 - rowers and 56 sportsmen who practice speed and power track and field exercises). The frequency of promotor polymorphisms and the 7th exon of the eNOS gene in athletes engaged in finswimming and throwing has been studied. The comparative analysis of the obtained data with the frequency of allel variants of the eNOS gene has been carried out in athletes engaged in speed-power sports and the individuals not going in for sports. To study the influence of polymorphisms of this gene on individual values of resistance to hypoxia, a gas analysis was conducted in the athletes practicing rowing. During the study the eNOS gene expression was examined in athletes practicing short-course underwater finswimming with apneapracticing long distance swimming with a snorkel.Results: The findings are evidence of a possible variant of influence of polymorphism of the eNOS gene on the phenotype formation resistant to exercise-induced hypoxia.Conclusions: In the athletes practicing underwater finswimming, the occurrence of the allelic variant of C/C T-786→C promoter polymorphism and T/T-variant in exon 7 of the gene of NO-synthase is lower than in the general population of Ukraine and in the athletes of speed and power type of sports, which may be the result of selection and be important for peculiarities of the development of resistance to exercise-induced hypoxia with different types of muscle activity.