Vacuolar myelopathy (VM) and tract pallor are poorly understood spinal tract abnormalities in patients with the acquired immunodeficiency syndrome (AIDS). We studied the ability of magnetic resonance imaging (MRI) to detect these changes in spinal cord specimens postmortem and whether criteria could be formulated which would allow these conditions to be differentiated from other lesions of the spinal cord in AIDS, such as lymphoma, cytomegalovirus (CMV) and human immunodeficiency virus (HIV) myelitis. We imaged 38 postmortem specimens of spinal cord. The MRI studies were interpreted blind. The specimens included cases of VM myelin pallor, CMV myeloradiculitis, HIV myelitis, lymphoma as well as normal cords, both HIV+ve and HIV-ve. MRI showed abnormal signal, suggestive of tract pathology, in 10 of the 14 cases with histopathological evidence of tract changes. The findings in VM and tract pallor on proton-density and T2-weighted MRI were increased signal from the affected white-matter tracts, present on multiple contiguous slices and symmetrical in most cases. The pattern was sufficiently distinct to differentiate spinal tract pathology from other spinal cord lesions in AIDS.