There is evidence for the involvement of the endocrine system in schizophrenia. This involment was widely investigated in female patients. In the current study, we examined prolactin and estradiol serum levels in hospitalized unmedicated men with first-episode and recurrent schizophrenia and then tested possible correlation with various subtypes of the disease. In addition, the estradiol and prolactin levels were compared with a healthy control group. The serum samples were assessed the morning following admission in fifty-seven schizophrenia male patients. There was a significant difference in prolactin serum levels between the paranoid and "nonparanoid" schizophrenia subgroups. However, no significant differences were found in estradiol serum levels between schizophrenia subtypes or between the patients and their healthy counterparts. Finally, a significant and positive correlation was found between the prolactin and estradiol levels in the paranoid subgroup alone. Thus, it appears that low estradiol levels are associated with low prolactin levels, alleged hyperdopaminergic tone and psychotic breakdown in paranoid schizophrenia. The results of the present study further support our previous report of the association between prolactin serum levels and the schizophrenia cluster subtypes, indicating a different dopaminergic activity for the various forms of the disease.