PURPOSE: To compare functional MR imaging of the motor cortex during active and passive movement. MATERIALS AND METHODS: Seven healthy, right-handed volunteers (M:F=6:1; age:25-30 years) were included in this study. A 1.5-T whole body scanner and the multislice EPI BOLD method were used. The motor paradigm was flexion-extension of a thumb against rest. In the active motion task, the thumb was flexed voluntarily once a second, while in the passive task, it was tied with a thread and pulled to flex and extend passively at the same interval and with the same intensity as in the active task. For image postprocessing, an SPM 96 program was used. The sites, numbers, and signal intensity of the activated pixels were determined, and the threshold for significance was set at p<0.001 to p<0.01. RESULTS: In the active motion task, strong activation at the contralateral side of the primary sensorimotor cortex and supplementary motor cortex occurred in all 14 examples in all seven volunteers. Additionally, the ipsilateral primary sensorimotor cortex and supplementary motor area were activated in 12/14 and 11/14 such tasks, respectively. During passive motion tasks, on the other hand, weak activation occurred at the contralateral side of the primary sensorimotor cortex in all cases, but in the contralateral supplementary motor cortex in only three. In the ipsilateral primary sensorimotor cortex and supplementary motor area, there was no activation. CONCLUSION: Compared with the active motion task, activation occurring in the contralateral primary sensorimotor cortex and supplementary cortex was weaker and less frequent during the passive task, and during this latter, the ipsilateral motor cortex remained inactive. These results may be useful for the clinical application of functional MR imaging in unconscious patients or in animal studies.