Frequency of promoter endothelial NO-synthase gene allelic polymorphism by using polymerase chain reaction and restriction fragment length polymorphism (RFLP-PCR) was determined in 221 patients with acute coronary syndrome (ACS) and in 83 almost healthy subjects. Data obtained indicate that different promoter allelic variant frequency differs significantly in patients with ACS and in control group. Correlation of normal homozygotes (T/T), heterozygotes (T/C) and pathologic homozygotes (C/C) was 48%, 36% and 16% respectively in patients, and in control it was 48%, 46%, 6% (P<0.05 by c2-test). Thus, in patients with ACS in Ukrainian population pathologic C/C variants of 5'-flanking region of eNOS gene were found 2.7-times more often in ACS patients, than in control. This allows us to suggest, that this allelic polymorphism can be considered as one of genetic risk factors of ACS development.