Aim. To asses the relationships between sociodemographic and clinical data and the bipolar spectrum features in treatment resistant patients. (A sub-analysis of data of the pilot study for the multi-center TRES-DEP (Treatment Resistant Depression) Project. Method. 50 drug-resistant 18-65 year old patients, fulfilling ICD- 10 criteria for depressive episode or recurrent depressive disorder(F32, F33) were included in the study. Drug resistance was defined as non-response to two adequate antidepressant treatments. The main exclusion criteria were: > 18 scores in the 17-item Hamilton Depression Rating Scale, treatment with mood stabilizers, the diagnosis of. substance misuse, dementia, severe neurological or other somatic disease. The presence of bipolar spectrum was detected by the Mood Disorder Questionnaire (MDQ) and the Hypomania Checklist Scale (HCL). Results. Statistically significant more drug-resistant patients fulfilling MDQ bipolar spectrum criteria (MDQ (+))comparing to patients without bipolar spectrum features by MDQ (MDQ(-)): 1) considered the last remission as partial or reported lack of remission (100% vs. 2 1%; p<0.05), 2) reported treatment non-adherence (41 vs. 18%, p=0.055). Moreover there were more suicidal attempts in MDQ(+) patients (0.86 +/- 1.28 vs. 0.25 +/- 0.59; p<0.05). Conclusion. Results of the study suggest that the presence of bipolar spectrum may worsen the course and outcome of drug-resistant depression. A further multicenter study is needed.