Acute and chronic ethanol administration results in a decrease in cellular Mg2+ content and an alteration of Mg2+ transport in liver cells. In this study we investigated the extent to which ethanol affects the Mg2+ transport mechanisms in the liver cell membrane. The functionality of these transport mechanisms was assessed in plasma membrane vesicles purified from livers acutely perfused with varying concentrations of alcohol, livers of animals fed with 6% ethanol for 3 weeks, and the respective controls. Acute alcohol administration had little or no effect on the Mg2+ extrusion mechanisms present in the apical and basolateral domains of the hepatocyte but completely impaired the Mg2+ entry mechanism present in the basolateral side of the cell. This effect was already evident at a dose of alcohol as small as 0.01% (approximately 1.5 mM). The chronic administration of ethanol, instead, impaired all the Mg2+ transport mechanisms irrespective of the location and directionality in a time-dependent manner. Taken together, these data indicate a selective sensitivity of the Mg2+ entry mechanism to acute alcohol administration, whereas the Mg2+ extrusion mechanisms are affected only after prolonged exposure to alcohol. These results suggest that the defect in hormone-activated Mg(2+) transport observed in the chronic EtOH model [Young, A., Cefaratti, C., & Romani, A. (2003). Chronic EtOH administration alters liver Mg2+ homeostasis. Am J Physiol 284, G57-G67] depends not only on a reduced cellular Mg2+ content but also on the impaired Mg2+ transport mechanisms present in the hepatocyte plasma membrane, in particular the Mg2+ entry pathway, which prevents the liver cell from restoring cellular Mg2+ homeostasis.