Until now, the pathogenesis of Marchiafava-Bignami disease, an extrapontine myelinolysis, is unknown. Accept an abuse of alcohol for many years additional metabolic and vascular disturbances are supposed. The early performance of magnetic resonance imaging in patients with a sudden encephalopathy and history of alcoholism is essential for an assessment of the diagnosis. The bilateral lack of transcallosal inhibition--a parameter for the integrity of the transcallosal connections between motor cortices--is the consequence of the axonal degeneration of transcallosal fibers. Clinical and neuroradiological features of three patients with extrapontine myelinolysis are reported and possible etiologies of the complex disease are discussed. In two cases a severe alcohol abuse was present with the typical picture of the Marchiafava-Bignami disease. In a third patient an intoxication with methanol was present with a similar clinical picture. Although severe neurological disturbances were initially apparent in the patients, during the follow-up there was a significant amelioration of the clinical course under a high-dose vitamin B supplementation.