Motor mapping using transcranial magnetic stimulation has been applied to the study of adaptive and restorative mechanisms of the motor cortex. To date, the reproducibility of mapping techniques has yet to be investigated in detail and/or confirmed. We report a technique used to map the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) motor cortices of 6 normal volunteers, each studied on 2 occasions separated by several weeks (range of 21-132 days). APB and ADM results were analyzed separately, with area and volume characteristics subjected to analysis of variance. Coefficients of variation, which should be low, ranged from 14% to 37% and coefficients of reliability, which should be high, ranged from 63% to 94%, indicating that the described technique for motor mapping is responsible.