Patients suffering from pain without evidence of either depression or organic lesions, or of any pathophysiological process to which the pain might be attributed, may be diagnosed as suffering from 'indeterminate pain.' The evidence in the literature which suggests that some of these cases might be due to a 'depressive equivalent' is examined. It is suggested that it is difficult, if not impossible, to formulate a diagnosis of depressive illness in patients who do not have clear symptoms of depression. However, there is evidence in the literature that a relatively high percentage of patients with chronic indeterminate pain appear to have a family history of depression and depressive spectrum disorders. Biological markers of depression also give some indication that certain of these patients may have a link with depressive illness as well as with pain. It is suggested that there is a need to explore the existence of a sub-group of patients with indeterminate pain in whom the mechanism of the pain may be related to the mechanism of depressive illness even though formal depressive symptoms are not found.