Pregnancy and lactation are phases during which major adaptations in maternal metabolism are necessary to meet the requirements of foetal growth and of lactation. Leptin, an adipocyte derived hormone, involved in regulation of energy metabolism, has been implicated in the coordination of these adaptive processes. Similar to monogastric species, increased leptin blood concentrations are reported for sheep at mid-pregnancy when compared to prebreeding, late pregnancy or early lactation (Ehrhardt et al., 2001). In sheep, the changes of leptin concentrations showed no obvious relation with the ability of insulin to promote glucose utilisation (Ehrhardt et al., 2001). With the study presented herein, we aimed to elucidate whether exogenous leptin modulates insulin responsiveness and whether the responsiveness is dependent of the physiological status of the animal. Using specific clamp techniques i.e. glucose infusion studies to quantify insulin secretion and resistance, we compared the effect of leptin application on glucose metabolism in pregnant versus lactating goats.