The superior temporal gyrus (STG) is strongly implicated in the pathophysiology of schizophrenia, particularly with regards to auditory hallucinations. In a previous study we reported a decrease in the density of M1 and M2/M4 muscarinic receptors in the STG in schizophrenia. In this study, we investigated the density of GABA(A) receptors in the left STG of schizophrenia patients compared to control subjects. We used quantitative autoradiography to investigate the binding of the agonist [(3)H] muscimol to GABA(A )receptors in the STG. A significantly higher density of [(3)H] muscimol binding was observed in the upper three quarters of the STG grey matter (corresponding to layers I-IV) than in the lower one-quarter (layers V-VI) in both groups. A significant increase (about 30%, P<0.05) in binding of [(3)H] muscimol was clearly observed in schizophrenia patients compared to control subjects. There were no significant correlations between [(3)H] muscimol binding density and age, post-mortem interval, brain pH or final recorded antipsychotic drug use. These results suggest an increase of GABA(A) receptor densities in the STG of schizophrenia patients.