Purpose: Transcranial magnetic stimulation (TMS) of the motor cortex can interrupt voluntary contralateral rhythmic limb movements. Using the method of resetting index (RI), our study investigated the TMS effect on different types of bimanual movements. Methods: Six normal subjects participated. For unimanual movement, each subject tapped either their right or left index finger at a comfortable rate. For bimanual movement, index fingers of both hands tapped in the same direction (inphase) or in the opposite direction (antiphase). TMS was applied to each hemisphere separately at various intensities from 0.5 to 1.5 times motor threshold (MT). TMS interruption of rhythm was quantified by RI. Results: For the unimanual movements, TMS disrupted both contralateral and ipsilateral rhythmic hand movements although the effect was much less in the ipsilateral hand. For the bimanual inphase task, TMS could simultaneously reset the rhythmic movements of both hands, but the effect on the contralateral hand was less and the effect on the ipsilateral hand was more compared with the unimanual tasks. Similar effects were seen from right and left hemisphere stimulation. TMS had little effect on the bimanual antiphase task. Conclusion: The equal effect of right and left hemisphere stimulation indicates that neither motor cortex is dominant for simple bimanual inphase movement. The smaller influence of contralateral stimulation and the greater effect of ipsilateral stimulation during bimanual inphase movement compared with unimanual movement suggest hemispheric coupling. The antiphase movements were resistant to TMS disruption, and this suggests that control of rhythm differs in the two tasks. TMS produced a transient asynchrony of movements on the two sides, indicating that both motor cortices might be downstream of the clocking command or that the clocking is a consequence of the two hemispheres communicating equally with each other.