Eight newborn piglets were randomly assigned to two groups. All of the piglets were fed with a milk replacer using an "artificial sow". Three times daily for six days they received physiological saline (0.9% NaCl) (control group, n=5) or leptin at 10 µg/kg body weight dissolved in physiological saline (experimental group, n=3) administered intragastrically. The piglets were then anaethesized, the entire gastrointestinal tract removed, and fragments of the duodenum and mid-jejunum were harvested and their in vitro motility was measured. Despite lack of differences in body weight, the piglets treated with leptin showed differences in the weight of the stomach and pancreas and length of the ileum in comparison with the controls. Administration of leptin also significantly affected intestinal motility in a manner characteristic of the particular segments (P < 0.05; P < 0.01; P < 0.001, respectively). The spontaneous contractions of the duodenum and its response to acetylcholine and isoproterenol were higher in the group of piglets treated with leptin than in controls, whereas segments of the jejunum behaved in the opposite manner. The experiments will be continued in order to confirm these results on a larger number of animals.