There is increasing evidence of endothelial dysfunction as the common underlying mechanism for the development of erectile dysfunction of vascular origin and as the triggering factor for the development of atherosclerosis and subsequent cardiovascular disease.To approach the controversy on the reliability and validity of proposed markers of endothelial dysfunction in a critical way, and to answer the question of whether detection of endothelial dysfunction in the laboratory, primarily in patients without clear symptoms of cardiovascular disease, is possible.A review of available published data in the most relevant papers for this topic identified from 1980 to May 2008 was performed, including data from our personal research and experience.It is important to develop a reliable laboratory marker of endothelial dysfunction. That marker would permit us to suspect or confirm relevant clinical questions in patients with erectile dysfunction: endothelial health, risks of future vascular episodes, response to treatments, and others.To date, multiple markers relevant to detection of endothelial dysfunction have been proposed. Nevertheless, reliability of endothelial function assessment will benefit from the integration of the different pieces of information provided by each marker. Detection of endothelial dysfunction in both the laboratory and clinical settings remains as a challenging opportunity.