This study explored the effects of acoustic noise on the cerebral asymmetry of speech perception. We measured magnetic fields of the brain elicited by consonant-vowel syllables in silence and white noise. Background noise affected brain responses to these stimuli differently in the left and right auditory cortices. Its depressive effect on cortical responses was found mainly in the left hemisphere, whereas the right hemisphere was unaffected or exhibited increased activity in noise. Locations of the P1, N1, and P2 activity sources in noise were different from those in silence in the right but not in the left hemisphere. These results suggest an increased right hemisphere role in speech sound processing in noisy conditions, involving the recruitment of additional right auditory cortex structures.