Several well-known observer scales, including the Hamilton Depression Scale (HAM-D), Montgomery-Åsberg Scale (MADRS), Major Depression Rating Scale (MDS), Melancholia Scale (MES), and Inventory for Depressive Symptomatology (IDS) used for measuring severity of depressive states have been compared by their responsiveness in an open trial including patients treated with a combination of citalopram and mianserin. The patients fulfilled the Diagnostic and Statistical Manual (DSM)-IV criteria for major depressive episode, and all scored 18 or more on the HAM-D before treatment. Onset of antidepressant action was defined as an improvement of rating scale scores of 25% or more of pre-treatment scores. A response to treatment was defined as a reduction of 50% or more on the pre-treatment scores. The results showed that the number of treatment days until improvement was 11 to 13 with no difference between the scales. The days until response were between 18 and 21 with no difference between the scales. In conclusion, the depression scales were found to be equal in their ability to detect changes in depressive symptoms during treatment. The mean of days to response was 19 for the combination of citalopram and mianserin. This is similar to the response for the combination of fluoxetine and pinolol.