13 patients with major depressive disorder, who responded well to the reversible MAO-A-inhibitor moclobemide after unsuccessful initial treatment with tri- or tetracyclic antidepressants were monitored under naturalistic outpatient therapy conditions with moclobemide plasma level control for an average of 7.4 months. Due to depressive relapse moclobemide treatment had to be discontinued for 6 patients. Increased dosages or the addition of a tricyclic antidepressant did not bring about any sufficient improvement. The relapse occurred after an average of 2-3 months of treatment with moclobemide administration. In the case of 7 patients it was possible to discontinue treatment with moclobemide after an average of 9.7 months with an incremental reduction in dosage. Recurring depressive symptoms were counteracted in the case of 2 patients by increasing dosages and adding a tricyclic antidepressant. The patients reported good tolerance of the drug as compared to tri- or tetracyclics.