Patterns of leptin secretion during the estrous cycle and the possible relationship of changes in circulating leptin during the periovulatory period with ovarian function in sows of obese (Iberian breed) and lean genotype (Large White x Landrace) were evaluated in two consecutive experiments. Plasma leptin concentrations throughout the estrous cycle in lean sows remain unchanged, but Iberian females showed a periovulatory increase in circulating leptin levels without associated changes in body condition and fatness. In these sows, plasma leptin concentrations at Days -1 and 0 of the cycle were found to be positively correlated with the ovulation rate (r=0.943 and r=0.987, respectively; P<0.05 for both), but the levels of leptin at Day 0 were negatively correlated with the progesterone release from Day 3 (r=-0.557; P<0.05) and, became more evident at Day 5 of the estrous cycle (r=-0.924; P<0.005). Such relationships were not observed in the females of the lean genotype. In conclusion, the present study indicates the existence of a distinctive pattern in the periovulatory leptin secretion in swine with obesity and leptin resistance, which is associated with the number and functionality of the corpora lutea present in the subsequent cycle.