AIM The main processes modulated by Ca and involved in the cause of schizophrenia are alteration in the dopamine and glutamate neurotransmitter system. Intracellular effects of Mg-ions are opposite to Ca-ions in competition at K-ion channels, in Na/K-ATP-ase activity, cAMP/cGMP concentration and Ca-ion currents in pre- and postsynaptic membranes. We conducted this research due to the incongruent results on Ca and Mg concentration that have been published until now and to determine platelet Mg concentration in suicidal and non-suicidal schizophrenic patients. METHODS A group of schizophrenic patients consisted of 23 patients with attempted suicide (S-SCH) and 48 patients without suicidal behavior (K-SCH) diagnosed according to ICD-10 diagnosis (F20.0) with or without intentional self-harm (X60-X84). The control group (K) included 99 healthy voluntary blood donors. The Mg and Ca concentration in platelets and serum was determined by atomic absorption spectrophotometry on the AAnalyst 200. RESULTS Using one-way anova test and manifold application of the Student-Newman-Keuls post-hoc test we established that there were higher concentrations of platelet Mg (μmol/109 platelets) (P=0.009, F=4.89) and lower concentrations of serum Ca (mmol/L) (P<0.001, F=19.18) in the S-SCH group of patients and higher concentrations of platelet Ca/Mg ratio in the K-SCH group of patients (P=0.006, F=5.37). CONCLUSION A higher Ca/Mg ratio in the platelets of non-suicidal patients confirms indirect higher Ca concentration. Higher Mg concentration in the platelets of suicidal patients, considered a Ca antagonist, may represent a compensatory attempt to restrain Ca activity.