One of the main points in the biological trends is, the circadian rhythm and disturbance in this cycle, which cause mood disorders and irregularity in this bio clock, to get depression. The pineal gland with the precise regulation of circadian rhythm of melatonin regulates the brain haemostasis. The abnormal function of this gland gives rise to psychiatric disorders.

In the period of youth and early of middle-age cause biochemical changes and disturbance in biorhythm including melatonin secretion.

This process can change the peak of melatonin phase. In addition, a decrease in the level of serum melatonin, can change the function of immune system of depressed patients. This function facilitates the process of cancerous cell formation and tumor growth.

With respect to the conflicting results and that the positive and negative roles of melatonin in the creation of depression is unknown, the aim of this study was to compare the morning and nocturnal serum melatonin rhythm levels in the patients with Major Depressive Disorder. The second purpose was to measure the morning and nocturnal serum melatonin levels in the depressed and healthy men and women.

Inclusion Criteria:

1. age: 22-48 years old
2. gender: male, female
3. who got a depressive score above 20, were included in the depressed group
4. those who obtained a depressive score below 9, were chosen and they were included in the healthy control group.
5. the healthy control group to match to the depressed patients for education, social occasion, occupational and economical situation.
6. the depression disorder was confirmed on the basis of the DSM criteria

Exclusion Criteria:

1. present or past psychiatric
2. physical diagnoses
3. drug consumption
4. use of narcotic substances
5. physical and psychosomatic disorders
6. the stressor
7. malfunction of thyroid gland
8. shift working

The individuals were chosen who referred to the industrial medical unit of one of big company.