A sample included 59 patients, 38 males and 21 females, mean age (M+/-SD) 33,4+/-10,2 years, age-at-onset 26+/-9,5 years, illness duration 7,8+/-6,1 years, with episodic progressive schizophrenia (ICD-10: schizophrenia, paranoid type, F20.0) with continuous course at the stage of exacerbation. Clinical symptoms were assessed using the PANSS. Platelet 5-HT content, 3H-serotonin uptake (Vmax), 3H-imipramine receptor density (Bmax), high- and low molecular weight human serotonin platelet transporter protein immunoreactivity (HMW-SERT and LMW-SERT values) were measured. The most frequent psychotic symptoms were delusions, conceptual disorganization and hallucinations, with the majority of patients experiencing from one to three symptoms. A significant increase of platelet 5-HT content and 3H-imipramine receptor density (Bmax) was found in male patients. In the male group, delusions, conceptual disorganization and hallucinations as well as PANSS psychotic cluster scores were correlated positively with 5-HT content and negatively with HMW-SERT and LMW-SERT values. Possible reasons of the differences in correlations of platelet 5-HT serotonin and serotonin transporter values with psychotic symptoms are discussed. The results are additional evidence for the involvement of serotonergic dysfunction in the pathogenesis of schizophrenic psychoses. They confirm the usefulness of testing of platelet 5-HT content and SERT immunoreactivity as biological markers of schizophrenic psychoses, in particular for male patents.