A brain magnetic resonance imaging (MRI) study of the corpus callosum in 36 normal volunteers, ages 26-79 years, revealed that age was positively correlated with the T1 spin-lattice relaxation time of the corpus callosum and was negatively correlated with the corpus callosum cross-sectional area. T1 relaxation times are sensitive to the content and macromolecular environment of tissue water, and variations in callosal T1 may reflect differences in the content or relaxation properties of callosal water. Such changes also potentially could occur secondary to alterations in the composition of callosal myelin. This study confirms and extends prior morphological studies that have reported age-related dimensional changes in the corpus callosum and, in addition, provides evidence of age-related biophysical tissue differences in the human corpus callosum.