The present study was carried out to determine polymorphonuclear (PMN) elastase levels and to explain whether or not altered levels may be a factor in depression. The patient group included a total of 68 patients with depression (32 with major depression, 36 with dysthymia). The control group included 40 volunteer, healthy subjects. WBC, erythrocyte sedimentation rate (ESR), immunogloblins (Ig A, Ig G, IgM), and complements (C3 and C4) levels of the patient and control groups were determined The mean PMN elastase levels, determined by immunoactivation method, in patients with major depression without and with melancholia, dysthymia and healthy subjects were found to be 99.5 (10.8) mu g/L [arithmetic mean (SEM)] 289.0 (71.3) mu g/L, 55.7(5.5) mu g/L, and 47.3(2.6) mu g/L, respectively. The mean PMN elastase level was found to be statistically higher in patients with depression, especially in patients with major depression, than that of healthy subjects, It was concluded that severe depression is associated with immunological and inflammatory alterations and the alterations may be showed easily by PMN elastase measurements.