Monoamine oxidase (mao)-inhibitors are often prescribed in patients suffering from treatment-resistant depression, but the evidence of its effectiveness in this type of depression is limited: a restricted amount of similar studies describes response-rates of 12-75%.<br/> AIM: To get more insight in the effectiveness of mao-inhibitors in treatment-resistant depression in clinical practice.<br/> METHOD: We investigated medical files of patients with a uni- or bipolar, treatment-resistant depression and looked at the difference in score on the Inventory of Depressive Symptomatology - Self Report (ids-sr) before and after 3 months of treatment with a mao-inhibitor. After that, we investigated how often patients achieved remission, response, partial response, no response or drop-out due to of side-effects.<br/> RESULTS: The included 17 patients achieved a mean decrease of 8.6 (sd:15.1) points, which corresponded with a decrease of 16.8% (p = 0.032). One patient (6%) achieved remission, 2 patients (12%) achieved response, 5 patients (29%) had partial response and 7 patients (41%) did not respond at all. Three patients (18%) quitted because of side-effects.<br/> CONCLUSION: The results of this and similar studies are modest and ask for critical thinking and critical prescribing of mao-inhibitors, because of the possibly limited effectiveness in treatment-resistant depressions.