Melatonin is an ancient molecule secreted at night by the pineal gland whose therapeutic properties have been increasingly investigated. Its beneficial effects have been studied in diverse malignancies, including ovarian cancer. Ovarian cancer (OC) is the leading gynecological cause of mortality in the United States. The chicken spontaneously develops OC with high incidence and mirrors the human disease. We evaluated the role of melatonin in OC using dietary melatonin supplementation and pinealectomy. With low dose dietary supplementation, we were able to increase nocturnal melatonin without altering its rhythm but failed to alter overall OC incidence. It is possible that the selected dosage may be insufficient or that malignant transformation occurred prior to enrollment date. Further studies using higher doses of melatonin or exploring chronic melatonin deficiency are underway and preliminary results are presented in Appendix I and II.