Continuous insulin infusion is sometimes used in very low birth weight infants with glucose intolerance. We studied the availability of insulin to the neonate by means of a laboratory-simulated clinical infusion under both flushed and non-flushed conditions. Although loss of insulin was noted with both solutions (0.5 U/ml), under the nonflushed condition only 55.9% of the prescribed dose for the first 2 hours was delivered before the delivery rate of the flushed system, 71.4%, was approached. These findings have implications for neonatal insulin administration.