We investigated structural changes of the corpus callosum in patients with Alzheimer's disease (AD) using sagittal diffusion-weighted (DW) and magnetization transfer (MT) imaging. Patients with AD (n=23) had a significantly decreased area only in the posterior portion of the corpus callosum. Apparent diffusion coefficient (ADC) values perpendicular to the commisural fiber orientation were significantly higher in the anterior portion of the corpus callosum without definite atrophy, as well as in the posterior portion with significant atrophy, in patients with AD than in controls (n=16) and thus diffusion in these regions showed a significantly lower degree of anisotropy in patients than in controls. MT ratios were also significantly lower in patients with AD in the anterior and posterior portions of the corpus callosum than in controls. These findings probably reflect structural changes in the corpus callosum including axonal loss and/or demyelination. DW and MT imagings may be useful in detecting degeneration of the corpus callosum in AD.