Leptin, primarily secreted by adipocytes, is a peripheral hormonal signal involved in the hypothalamic integration of energy homeostasis. We report that plasma leptin levels fluctuated in a pulsatile fashion in gonad-intact adult female and male rats. Whereas in male rats leptin was secreted in the form of low-amplitude, high-frequency pulses, in female rats high-amplitude pulses were secreted at only a slightly lower frequency. Consequently, plasma leptin concentrations were higher in female than in male rats. Gonadectomy decreased leptin secretion but the sexually dimorphic leptin pulsatility pattern persisted. These results show that there is a distinct female-type and male-type leptin pulsatility pattern and each is amenable to augmentation by gonadal steroids either involving mechanisms that impart leptin pulsatility patterns directly at the level of adipocytes and/or at hypothalamic target sites.