The article reviews the assessment of endothelial function in humans, discussing various methods and their clinical implications. Endothelial dysfunction, characterized by an imbalance between vasodilating and vasoconstrictive factors, is associated with cardiovascular risk factors and is a key pathological condition. While endothelial function can be measured non-invasively, its use in daily clinical practice is not yet established. The review covers methods such as coronary angiography, intravascular ultrasound, and flow-mediated vasodilation (FMD) of the brachial artery. FMD is widely used but requires standardized protocols. Finger plethysmography (EndoPAT) is another non-invasive method that measures arterial volume changes. Endothelial dysfunction is a marker for cardiovascular risk and provides prognostic information beyond traditional risk scores, particularly in patients with established coronary disease or those at high risk. It can also help identify responders and non-responders to therapy. However, the role of endothelial function in drug development and its potential to guide treatment remains under investigation. The article concludes that while endothelial function measurements provide valuable additional information, their clinical utility in daily practice requires further research to determine if they can improve patient outcomes.The article reviews the assessment of endothelial function in humans, discussing various methods and their clinical implications. Endothelial dysfunction, characterized by an imbalance between vasodilating and vasoconstrictive factors, is associated with cardiovascular risk factors and is a key pathological condition. While endothelial function can be measured non-invasively, its use in daily clinical practice is not yet established. The review covers methods such as coronary angiography, intravascular ultrasound, and flow-mediated vasodilation (FMD) of the brachial artery. FMD is widely used but requires standardized protocols. Finger plethysmography (EndoPAT) is another non-invasive method that measures arterial volume changes. Endothelial dysfunction is a marker for cardiovascular risk and provides prognostic information beyond traditional risk scores, particularly in patients with established coronary disease or those at high risk. It can also help identify responders and non-responders to therapy. However, the role of endothelial function in drug development and its potential to guide treatment remains under investigation. The article concludes that while endothelial function measurements provide valuable additional information, their clinical utility in daily practice requires further research to determine if they can improve patient outcomes.