Despite the important role breastfeeding plays in regulating a mother's fertility, the mechanisms controlling lactational infertility remain to be fully elucidated. Breastfeeding suppresses fertility for a period which varies widely among individuals and within different communities. Suckling stimulus is the key factor in controlling the duration of infertility. Suckling by the infant appears to inhibit luteinizing hormone secretion by inhibiting the pulsatile release of gonadotrophin-releasing hormone from the hypothalamus. The exact mechanism remains unclear but a suckling-induced increase in hypothalamic opioid tone may be involved. Prolactin does not appear to play a major role, other than being essential for maintenance of milk production, in lactational infertility.