The Major Depression Rating Scale (MDS) has been derived from the Hamilton Depression Scale and the Melancholia Scale. The MDS contains the nine DSM-IV items for major depression which all have anchoring scores from 0 to 4; hence, the theoretical score range is up to 36. The Major Depression Rating Scale has in this study been psychometrically analysed in randomized moclobemide trials. The results showed that the MDS had higher internal validity than the Hamilton Depression Scale. Thus, the homogeneity of the items was higher; factor analysis identified only one general depression factor (after 4 weeks of treatment explaining more than 50% of the variance). The inter-rater reliability of the two scales was of the same high level. The ability to measure changes (external validity) was tested in randomized clinical trials with moclobemide versus tricyclics (clomipramine and notriptyline) performed in Denmark in the psychiatric setting as well as in the general practice. The results showed that in the psychiatric setting tricyclics were superior to moclobemide with effect sizes ranging between 0.43 and 0.53. The highest effect size was obtained with the Melancholia Scale and the Major Depression Rating Scale, while the Hamilton Depression Scale was below 0.50. In the general practice setting no difference was found between moclobemide and clomipramine. In conclusion, the Major Depression Rating Scale has been found to have a more homogeneous factor structure than the Hamilton Depression Scale, but still with the same level of reliability and external validity. However, studies are needed to standardize the scale, especially in the general practice setting.