To investigate interhemispheric interaction (IHI), the EEGs of 42 children between the ages of 7-8 years were recorded while they were performing, as fast as possible, both unimanual and bimanual rhythmic tapping tasks. As an EEG index of IHI we used coherence values (Coh) in the alpha band in the pairs of leads F3/F4, C3/C4, P3/P4, O1/O2, and T3/T4 during resting and tapping. The difference between left hand (L-L) and right hand (R-R) intertap intervals in comparable conditions was though to reflect IHI. Interhemispheric alpha Coh increase was only evident in bimanual rhythmic tasks, and was confined to the C3/C4 and P3/P4 regions. Coh in these brain areas correlated negatively with the time difference between the L-L and R-R intertap intervals. The results show that interhemispheric alpha Coh. can be regarded as an index of IHI during bimanual tapping, and support the clinical hypothesis that bimanual versus unimanual tapping might reflect interhemispheric or callosal function.