Functional alterations in the central serotonergic system, including presynaptic and postsynaptic function, have been reported in schizophrenia. Recently, there have been conflicting reports that the increase in plasma cortisol or prolactin concentrations induced by meta-chlorophenylpiperazine (mCPP) was significantly blunted in schizophrenic patients compared with normal volunteers. Studies of the behavioral effects of mCPP, a serotonin (5-HT) receptor partial agonist with high affinity for 5-HT1C binding sites, have also yielded conflicting results in schizophrenic patients. The purpose of this study was to examine plasma levels of prolactin and cortisol, body temperature, and behavioral responses to mCPP and placebo in a single-blind study in 25 schizophrenic and 15 normal men. No differences either between schizophrenic patients and normal volunteers or between paranoid and undifferentiated/residual subtypes of schizophrenia were found in mCPP-induced prolactin, cortisol, or temperature responses. Schizophrenic patients and normal volunteers reported significant increases in feeling calm and feeling strange of comparable magnitude following mCPP. No significant differences between normal volunteers and schizophrenic patients were found in post-mCPP behavioral ratings, such as anxiety, irritability, depression, restlessness, or arousal.