In 10 premature infants (1123 +/- 263 g), fentanyl citrate (30 to 50 microgram/kg) was used in conjunction with pancuronium (0.1 mg/kg) as the sole anesthetic for transthoracic ligation of patent ductus arteriosus. Ventilation was controlled with air and oxygen in concentrations sufficient to maintain transcutaneous PO2 between 50 and 70 torr. Circulatory stability was easily maintained throughout the procedure. "Stiff chest" was avoided by the use of muscle relaxants, and the infants were awake within 1 hour after the procedure.