The role of leukocytes and cytokines in ovarian physiology is now established, although the function of each cell type and cytokine remains to be determined in detail. Current knowledge of these effects on follicle development, ovulation, luteinization and luteotrophic process and luteolysis is reviewed. It is possible that further research will help to unravel some of the clinical mysteries in ovarian function, including polycystic ovary syndrome, premature menopause, ovulatory disorders, and luteal phase defect. Furthermore, the increasing use of cytokines and their antagonists in clinical practice may have significant effects upon reproductive function.