The authors searched for correlations between amounts of platelet proteins and results of psychometric tests in patients with the first episode psychosis (schizophrenia, schizoaffective psychosis) in the course of their combined antipsychotic treatment with haloperidol and clozapine. Psychometric evaluations (PANSS, BPRS) and analyses of platelet enzymes - glutamine synthetase-like protein (GSLP), glutamate dehydrogenase (GDH), and cytochrome c-oxidase (COX) - were carried out before, during, and after the treatment. These proteins were also analyzed in matched controls. All the parameters comprised a database, followed by statistical data processing using Statistica 6.0 (StatSoft) software, nonparametric statistics module. The patients before the treatment, when compared with controls, demonstrated significantly decreased COX activity (p=0,0000001) and increased GSLP amount (p=0,006) with a positive correlation between GSLP amount and PANSSneg (R=0,34, p<0,01). Those patients who displayed initially low COX activity (below median) demonstrated significant increase in COX activity after the treatment. Negative correlations were revealed between COX activity and PANSS, PANSSpsy scores during the treatment, i.e. the lower was COX activity, the more severe syndromes were observed. Negative correlations were found between the initial COX activity and PANSS, PANSSpsy, BPRS scores after the treatment, i.e., the higher was COX before the treatment, the less prominent syndromes were observed after the treatment. Significantly more "non-responders" by PANSSneg were found among the patients with low GSLP level (below median) than their calculated expected amount. The COX activity measured before the treatment was significantly lower in patients with schizophrenia than in patients with schizoaffective disorder (SAD) (p=0,038). In SAD patients, the initial COX activity was negatively correlated with PANSSpsy and BPRS scores after the treatment (R=–0,5, p=0,02), i.e. the lower was the COX the activity before the treatment, the more prominent syndromes were observed after the treatment.