We studied the sensitivity in detecting changes of the 6-item version of the original 17-item Hamilton Depression Rating Scale (HAM-D) and compared it with the more widely used versions among 164 depressed outpatients with and without atypical features before and after treatment with fluoxetine. The 6-item HAM-D was shown to be as sensitive as the 17-, 21- and 24-item versions of this scale. In addition, the different versions of the HAM-D were strongly correlated with each other at baseline and at the endpoint. It appears that the 6-item version of the HAM-D allows the assessment of severity of depression with comparable sensitivity to the standard and more elaborate versions of the same scale.