Verbal auditory hallucinations are common in schizophrenia but little is known about how they arise. We have used single photon emission tomography (SPET) to measure regional cerebral blood flow with the aim of identifying brain areas that are especially active during auditory hallucinations. We scanned twelve men with schizophrenia while they were experiencing hallucinations. The subjects were rescanned under identical conditions when their hallucinations had resolved (mean 19 weeks later). Blood flow was significantly greater during hallucinations than in the non-hallucinating state in Broca's area (mean count density on SPET 1.18 [SD 0.04] vs 1.13 [0.06]; p < 0.001); flow was also higher during hallucinations in the left anterior cingulate cortex and regions in the left temporal lobe, but these differences did not achieve significance. The increased flow in Broca's area was not accounted for by changes in other clinical variables nor by changes in the dose of neuroleptic drugs. These findings suggest that the production of auditory hallucinations in schizophrenia is associated with increased activity in a network of cortical areas specialised for language.