OBJECTIVE: Auditory hallucinations are a serious problem for a large subgroup of psychotic patients who do not respond optimally to neuroleptic medication. It has been hypothesized that hearing imaginary voices involves the same physiological processes as those involved in hearing real voices, but this hypothesis has not been conclusively confirmed. METHOD: In this study a consonant-vowel version of the Dichotic Listening Test was used to assess the functional integration of the left hemisphere in hallucinating and nonhallucinating psychotic patients. The test was administered under three conditions: a nonforced attention condition, a condition in which attention was forced to the left ear, and one in which attention was forced to the right ear. RESULTS: The nonhallucinating patients showed the normal right ear advantage, which indicates a left hemisphere superiority in the processing of linguistic stimuli. In contrast, the hallucinating patients showed no ear advantage. Neither group was able to modify its performance when instructed to attend to either the left or the right ear. A subgroup of patients was tested in both hallucinating and nonhallucinating states, but the ear asymmetry was not noticeably different between these states. CONCLUSIONS: The results suggest that auditory hallucinations are associated with abnormalities in left hemisphere functioning and that these abnormalities might not be limited to the time of the auditory hallucinations. It is hypothesized that a relatively enduring left hemisphere abnormality may leave some patients at risk for auditory hallucinations.