lntrauterine growth restriction (IUGR) may be accompanied by inadequate thermoregulation, especially in piglets that are not considered to possess any brown adipose tissue (BAT) and are thus entirely dependent on shivering thermogenesis in order to maintain body temperature alter birth . This due to an open-reading frame on the BAT specific uncoupling protein (UCP)1 gene in the porcine species meaning UCP1 is not expressed. The onset of non-shivering thermogenesis in BAT at birth is dependent on the rapid appearance of endocrine stimulatory factors, including leptin . Leptin can stimulate heat production by promoting non­shivering thermogenesis in BAT, but whether this response occurs in piglets is unknown. Newborn female piglets thal were characterised as showing IUGR (mean birth weight of -0.98 kg ± 0.26: n=48) were therefore injected with either saline or leptin once a day for the first live days of neonatal life. The dose of 5leptin was 0.5 mg/kg which is sufficient, as previously, to increase plasma leptin -10 fold and on the shown day of birth induced a rapid increase in body temperature to values comparable with normal sized "control" piglets (mean birth weight of -1.47 kg ± 0.37: n=26). Perirenal adipose tissue was then sampled from all offspring at 21 days of age and presence of the BAT specific uncoupling protein (UCP)1 determined by immunohistochemistry and immunoblotting. UCP1 was clearly delectable in all samples analysed and its abundance was significantly reduced in the IUGR piglets administered saline compared with controls, but was raised to the same amount as controls in those IUGR lemales given leptin. There were no differences in gene expression between primary markers of brown and white adipose tissue between groups. ln conclusion, piglets possess BAT that when stimulated exogenously by leptin can promote body temperature.