Patients with chronic psychogenic pain appear to suffer from a specific depressive type of disease, with somatized pain as the prime expression of a concealed mental agony (pain-prone disorder). This view is supported by clinical, premorbid, and psychodynamic findings, as well as by the presence of biological markers including a family history of affective disorders and response to antidepressants. Additional biological markers of depression include shortened rapid eye movement (REM) latency in sleep and nonsuppression in the dexamethasone suppression test (DST). The study of both markers in 20 consecutive pain-prone patients with insomnia showed clearly abnormal REM latency and/or DST nonsuppression in one half of the otherwise homogeneous group. There was high correlation between DST cortisol level and REM latency. both biological markers tend to predict response to antidepressants. The findings confirm that the pain-prone disorder can be viewed as a variant of depressive disease.