 The present study evaluated the relationship between Stanate dose, drug safety, and efficacy in a non randomised sequential open label cohort design, in 55 patients. Subjects were term and near term infants at medium or high risk of hyperbilirubinemia with TSB levels approaching the threshold for exchange transfusion. The first cohort began at a dose of stannsoporfin 0.75 mgkg of birth weight intramuscularly. The dose was then increased to 1.5 mgkg for cohort 2, and saline was given placebo for cohort 3. Safety evaluations consisted of hepatic, renal and hematologic clinical laboratory tests along with serial physical examinations. Long term follow up of all patients to age 6 is planned. 