The aim of the study was to evaluate the prolactin levels in schizophrenic inpatients receiving antipsychotics. The levels of prolactin have been measured in 67 patients two times during hospitalization. The study has revealed hyperprolactinemia in almost all patients (regardless of gender) treated with conventional neuroleptics, sulpiride or risperidon. Clozapine and quetiapine have been proved to exert the least influence or the secretion of prolactin. No correlation between the clinical symptoms resulting from hyperprolactinemia and the prolactin level has been established. The study revealed the coexistence of hyperprolactinemia and extrapiramidal symptoms. This leads to the conclusion that hyperprolactinemia may result from that the optimal dosage for an individual patient has been exceeded.