The effect of ritodrine hydrochloride (RH) on bilirubin metabolism in newborn Wistar rats was studied. Wistar rat pups were given two 35-mg/kg injections of RH, and total bilirubin formation (TBF) was determined from the whole body excretion rate of carbon monoxide (VeCO). Early labeled bilirubin formation (ELB), plasma bilirubin levels, and hepatic heme oxygenase (HO) activity were also determined. We found significant increases in TBF, ELB, and HO in the RH-treated animals over the control animals. These increases, however, were small, considering the high doses of RH administered. Our findings suggest that at clinically administered doses, the potential for RH to exacerbate neonatal jaundice is minimal.