Background: The mechanism of vasodilation, caused by acetilcholine (ACh) stimulates the release of different substances from endothelial cells: endothelium-derived hyperpolarizing factor and endothelium-derived relaxing factor – nitric oxide (NO) and prostacyclin. The deficiency of NO may be the result of reduced expression or impaired activity of the enzyme eNOS, deficiency or reduced cellular uptake of L-arginine, elevated arginase activity, increased degradation of NO by endogenous inhibitors or by reactive oxygen species. Some of those processes are associated with aging and might lead to the development of cardiovascular diseases. The aim of the present study was to determine changes of endothelium-dependent and endothelium-independent vasodilation in the course of aging. Methods: We measured laser Doppler (LD) flux of cutaneous microvessels on the ventral side of the forearm. The endothelium-dependent and endothelium-independent vasodilation was determined in 81 healthy subjects divided into four age groups. In the first group there were 32 subjects aged 20-28 years, in the second 19 subjects aged 29-39 years, in the third 19 subjects aged 40-49 years and in the fourth 17 subjects 50-74 years old. The endothelium-dependent vasodilation was assessed by ACh iontophoresis and the endothelium-independent vasodilation by sodium nitroprusside iontophoresis. Data were analysed using ANOVA followed by Dunnett’s test. The study was approved by the National Medical Ethics Committee; written informed consent was obtained from each subject. Results: With aging maximal LD flux during endothelium-dependent vasodilation in three groups did not differ. In response to ACh application LD flux increased 9.94 ± 1.1times in the group aged 20-28 years; 10.7 ± 1.3 times in the group aged 29-39 years, and 10.5± 1.7 times in the group aged 50-74 years. In the group of subjects aged 40-49 years LD flux increased significantly less (5.38 ± 1.0 times). On the contrary maximal LD flux during endothelium-independent vasodilation decreased with aging (LD flux increased 11.5 ± 1.4 times in the group aged 20-28 years, 6.12 ± 8.3 times in the group aged 29-39 years, 6.43 ± 8.9 times in the group aged 40-49 years and 3.85 ± 7.4 times in the group aged 50-74 years). Conclusion: The endothelium-dependent vasodilation is mainly independent of age. The group of subjects, where endothelium-dependent vasodilation is smaller is the group in the period of greatest hormonal changes. The endothelium-independent vasodilation decreases with aging. From the observed results it can be concluded that other mechanisms that substitute diminished effect of NO as, for example, an increased release of prostacyclin or EDHF might be involved in endothelium-dependent vasodilation of aged subjects.