Recently, there has been considerable interest generated in the possible importance of magnesium ions (Mg2+) in the regulation of bronchial smooth muscle tone and pulmonary vascular tone. These factors have aroused interest in the possible utilization of Mg salts in the treatment of lung diseases (e.g., asthma, allergies, and pulmonary hypertension). Evidence is reviewed which indicates that Mg2+ can influence bronchial vasomotor tone, both indirectly and directly, as well as pulmonary vascular muscle contractility, mast cell granulation and neurohumoral mediator release. In addition, new experimental data suggest that Mg2+ influences a variety of lung structures and chemicals (e.g., capillary endothelial cell integrity, number of type II epithelial cells, surfactant, etc.). Surprisingly, pulmonary arterial muscle cells have a lower Mg content compared to other types of blood vessels and the myocardium, which might point to the vulnerability of the lung vasculature to lower than normal dietary intake of Mg. Several clinical reports point to the salutary actions of Mg2+ in asthma and asthma-like conditions. Very recent experimental findings in rats indicate that Mg2+ treatment can prevent development of experimental chemically induced pulmonary hypertension. Hypoxic pulmonary vasoconstriction has been reported to be attenuated by Mg2+. Although it is not clear as to whether dietary Mg2+ deficiency plays a role in development of some asthma-like conditions or pulmonary hypertension, Mg salts certainly appear to be potentially useful therapeutic avenues for these conditions and should be thoroughly investigated, both from clinical as well as experimental points of view.