OBJECTIVE: Most newborn infants with hyperbilirubinemia have gastrointestinal tract symptoms. The aim of this study is to investigate the effect of hyperbilirubinemia on gastrointestinal hormone levels in newborn infants. METHODS: Fasting plasma motilin and serum gastrin levels were measured using a radioimmunoassay in 50 term newborns with hyperbilirubinemia (Hyperbilirubinemia group). Fasting plasm motilin and serum gastrin levels from thirty normal term newborns were used as controls. RESULTS: The plasma motilin level in the Hyperbilirubinemia group (659±37 ng/L) was significantly higher than that of the controls (486±28 ng/L) (P< 0.01). The plasma motilin level was positively correlated with the serum bilirubin level. The serum gastrin level in the Hyperbilirubinema group was not different from that of the controls. CONCLUSIONS: The plasma motilin level is correlated with the level of bilirubin in the newborn. The abnormal increase in the level of motilin may be related to the development of gastrointestinal symptoms newborns with hyperbilirubinemia.