Neuroscientists have constantly sought new methods of evaluating brain function, with progressive improvement in the last century in imaging brain structure and function. However, except for direct surgical stimulation, neuropsychiatrists can only infer causality between the signal obtained on an image and a behavior or disease. Transcranial magnetic stimulation (TMS) is a new, noninvasive technique for directly stimulating cortical neurons. It has been used to map attention, memory, movement, speech, and vision. Preliminary investigations have also used rapid-rate TMS to improve motor speed in Parkinson's disease and mood in depression. TMS is likely to be an important future neuropsychiatric tool.