The superior temporal gyrus (STG) is strongly implicated in the pathophysiology of schizophrenia,particularly with regards to auditory hallucinations. In this study, using in situ quantitative autoradiography in postmortem tissue, we investigated the binding of the [3H]ketanserin to 5-HT2A receptors and [3H] mesulergine to 5-HT2C receptors in the left STG of 8 male schizophrenic patients compared to 8 control subjects. A strong [3H]ketanserin binding was observed in the STG, however there was a very weak [3H] mesulergine binding in the STG. A significant decrease in binding of [3H]ketanserin was clearly observed in schizophrenia patients in comparison with control subjects. There were no significant correlations between 5-HT2A binding density and age, postmortem intervals, or brain pH. These results suggest that the alterations of the 5-HT2A receptors contribute to the pathophysiology of the STG in schizophrenia. Furthermore, there is a clear tendency for a positive correlation between 5-HT2A and muscarinic M1 receptor bindings, and for negative correlations between 5-HT2A and GABAA receptor bindings and between muscarinic M1 and GABAA receptor bindings. This provides a possible mechanism of auditory hallucinations through interactions between 5-HT2A, acetylcholine muscarinic and GABA transmissions in the STG in schizophrenia.