WE measured regional cerebral blood flow (rCBF) during unimanual and bimanual movements using H215O PET. Six healthy volunteers performed unimanual, bimanual-symmetric and bimanual-asymmetric ballistic finger movements. The study was designed to minimize anticipation and preparation of movements. Data were analysed using SPM. Unpredictably paced unimanual movements resulted in significant activation of contra-lateral primary motor-somatosensory cortex (M1-S1) and mesial frontal cortex (p≤ 0.001). Performance of symmetric bimanual movements resulted in bilateral activation, but no additional activation of mesial frontal cortex was shown. Comparison of asymmetric with symmetric bimanual movements revealed additional recruitment of mesial frontal cortex (p≤ 0.001). We suggest that rostral mesial frontal cortex facilitates asymmetric non-mirrored bimanual finger movements.