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The authors investigated the oscillatory changes induced by auditory language task to assess hemispheric dominance of language. Magnetoencephalography studies were conducted during word listening in 6 normal right-handed volunteers and 13 epilepsy patients who underwent Wada test. We carried out a time-frequency analysis of event-related desynchronization (ERD)/event-related synchronization (ERS) and intertrial coherence. We localized ERD/ERS on each subject’s magnetic resonance images using beamformer. We compared ERD/ERS values between the left and right side of regions of interest in inferior frontal and superior temporal areas. We assessed the target frequency range that correlated best with the Wada test results. In all normal subjects, gamma ERD was lateralized to the left side in both the inferior frontal and superior temporal areas. In epilepsy patients, the concordance rate of gamma ERD and the Wada test results was 76.9% for the inferior frontal area and 69.2% for the superior temporal area. Gamma ERD can be considered as an indicator of language function, although it was not sufficient to replace the Wada test in the evaluation of epilepsy patients. The gamma ERD value of the inferior frontal area was more reliable for the assessment of language dominance compared with that obtained in the superior temporal area.