Dietary magnesium (Mg) intake has been shown to be independently related to lung function, airway reactivity, and respiratory symptoms in the general population. Inhaled Mg and IV Mg administration have been shown to promote bronchodilation and to improve lung function in asthmatic patients. Some studies have suggested that COPD patients exhibit decreased body levels of Mg. The purpose of the present study was to investigate the effects of acute IV Mg loading on parameters of respiratory function and maximal exercise capacity of stable COPD patients.The study hypothesis is that Mg administration will be associated to improvements on airflow and vasodilation leading to improvements of pulmonary function and exercise performance.