Fifty patients suffering from depression were treated wigh mianserin in monotherapy. ICD-9 and DSM-III criteria for depression were used. Patients were divided into four groups--with monopolar depression (28 patients), bipolar depression (8 patients), organic depression (10 patients), neurotic depression (4 patients). The intensity of psychopathological symptoms of depression was established using the Hamilton Depression Rating Scale (HDS) on the 7th, 14th and 28th day of the treatment. The antidepressant action of mainserin was evident already on the 14th day of treatment. Mianserin proved to be most effective in endogenous bipolar depression group and neurotic depression group (70% reduction in the score obtained on the HDRS). Mianserin was well tolerated by most patients. Most frequent side effects observed were: hypertension (8 patients), feeling of anxiety (10 patients), constipation (8 patients), tachycardia (6 patients), dry mouth (3 patients).