This study highlights the difficulties that may be encountered in attempting to apply the clinical construct of endogenous depression derived from western studies to depressed Arab patients. The agreement between 4 operational systems on the diagnosis of endogenous (melancholic) depression is explored in 100 patients with primary depressive disorder in Al-Ain, United Arab Emirates. The symptom characteristics of the 61 patients in whom all diagnostic systems agreed are then described quantitatively and qualitatively. Subjects were evaluated by the Newcastle scale, Hamilton's 21 item depression scale, global assessment of functioning scale, and the operational criteria of the diagnostic systems used. Diagnosis of endogenicity was derived by computer according to the respective criteriThe agreement between DSM-IV, ICD-10, and RDC criteria is moderately high (0.72). When the Newcastle Index is included, it is only moderate (0.58). Disagreements are related to differences in diagnostic criteriSmall differences affect concordance appreciably. DSM-IV agreed with a majority of external validators, differentiating a more homogeneous groups of patients. In the present study, endogenous depression identified by western criteria, was less likely to manifest by guilt feelings, a distinct quality of mood, and loss of libido. The descriptions of patients reveal that the mood component of depression is expressed differently, somatic metaphors are used frequently to express distress, religious elements influence the expression of 5 symptoms, and depression may manifest in behaviours not directly indicative of the disorder. Endogenous depression may be identified in the Arab culture, but considerable variation in its component symptom frequencies and mode of expression needs to be taken in consideration for defining it in terms appropriate to the culture.