Functional MR imaging using the blood oxygen level dependent technique as an endogenous contrast agent localizes eloquent cortex when stimulated by a variety of motor or sensory tasks. To date, visual, motor, speech, and cerebellar studies have been conducted, revealing significant information regarding cortical localization and control of various functions. The technique is also an important management tool for localizing eloquent cortex contiguous to a tumor or arteriovenous malformation, so that injury can be avoided if ablation of the lesion is contemplated.