Phosphorus magnetic resonance spectroscopy was used to determine effects of acute and chronic alcohol exposure on brain intracellular free magnesium concentration (Mgf) and bioenergetic state in rats. Acute alcohol (3 mg kg-1, i.p.) resulted in a transient ( < 2h) decline in brain Mgf and cytosolic phosphorylation ratio, and an increase in mitochondrial oxidative capacity. In contrast, chronic exposure to alcohol for 30 days by vapour inhalation resulted in a depletion of brain Mgf with no significant change in bioenergetic parameters. Subsequent exposure of chronically alcoholised rats to an acute dose of alcohol (3 g kg-1) did not result in any further changes. We conclude that chronic exposure to alcohol results in a depletion of brain Mgf and compromised bioenergetic regulation.