In patients with chronic idiopathic pain disorders we have analysed the construct validity of the Melancholia Scale as compared to the results with the scale in primary depression. The patients (n= 253) were treated in a placebo controlled trial with either clomipramine or mianserin independently of the Melancholia score. The construct validity of the Melancholia Scale was further analysed by the testing of the intensity model of depression versus anxiety using the Beck Depression Inventory, the Hamilton Anxiety Scale, the Spielberger State-Trait Anxiety Scale, and the Melancholia Scale. The construct validity in terms of scale homogeneity was analysed by Loevinger coefficients which can be considered as a latent structure evaluation. The Melancholia Scale showed acceptable homogeneity, while the Hamilton Anxiety Scale lacked sufficient homogeneity. In total, 33% of the patients had a score of 10 or more on the Melancholia Scale (corresponding to 13 or more on the Hamilton Depression Scale). The predictive validity of the Melancholia Scale was evaluated using active treatment versus placebo response after 6 weeks of therapy. It was shown that in patients with a Melancholia Scale score of 10 or more (corresponding to “less than major depression”) 72% had full recovery when treated with clomipramine, while 36% of the placebo treated patients obtained a full recovery (P≤0.05). The patients treated with mianserin obtained a full recovery in 52%. The group of patients with a Melancholia Scale score of 10 or more scored higher also on the anxiety scales indicating that the relation between depression and anxiety is a matter of severity. The depressed patients had significantly lower imipramine binding sites than the non-depressed patients.