The Polish TRES-DEP study assesses a number of demographic, clinical and psychometric features comparing patients with treatment-resistant and treatment non-resistant depression. The study included 1083 patients with single or recurrent depressive episode among which 570 met the criteria for treatment-resistant depression, on account of lack of significant improvement following at least two adequate courses of antidepressant treatment. All 1083 patients were assessed by means of the Polish version of Hypomania Check List 32 Scale. The Cronbach's alpha for entire scale was 0.94 which indicates high degree of consistency. Exploratory factor analysis resulted in five factors, of which the biggest (mostly overactivity and elation) containing items1-6, 7-19, 21, 23 and 27 had eigenvalue 10.95 and accounted for 34.2% and the second (irritability), items 25-26, with eigenvalue 2.92, accounted for 9.1% of total variation. Significant differences were obtained between patients with treatment-resistant and treatment non-resistant depression as to the scores of HCL-32. The mean score of HCL-32 was significantly higher in treatment-resistant vs non-resistant depression (11.9±8.3 vs 8.8±7.7, respectively, p< 0.001). Also, the percentage of patients having positive response to 14 or more items of the scale was significantly higher in treatment-resistant than in non-resistant depression (44% vs 29%, respectively, p< 0.001). Based on the results of HCL-32 scale, it may be concluded that the features of bipolarity make the patient more resistant to antidepressant treatment.