In the pharmacotherapy of psychiatric disturbances valproic acid (valproate) is very often applied in combination with other psychotropic drugs. The purpose of this study was to assess the level of valproic acid (VPA) in serum of the patients subjected to the monitoring of the drug concentration. 130 patients, in 2 years of the observation, have been examined. All patients were treated with VPA in combination with neuroleptics (I or II generation) or antidepressants. The range of VPA concentration, determined by FPIA method did not show significant differences in the studied groups of patients. Among all results obtained, 39% indicated VPA concentration on a subtherapeutic range with the mean value: 34,4 ± 11,2 µg/ml, 58% were within the limits of the therapeutic range (50-100 µg/ml) with mean value: 66,7 ± 11,3 µg/ml and 3% on a potentially toxic range (mean: 107,9 ± 6,6 µg/ml).The authors conclude that therapeutic monitoring of VPA concentration is useful in the patients submitted to polypharmacotherapy, and they indicate that it is necessary to limit polypragmasy, because of its influence upon the efficacy and safety of the treatment.