Medical personnel in a pediatric center were tested for their ability to correctly compute drug doses for sick newborns. One of every 12 doses computed by 95 registered nurses contained an error that would result in the administration of an amount that was ten times higher or lower than the dose ordered. The error rate was no different for experienced or inexperienced nurses. The test also included an evaluation of the nurse's ability to judge the appropriateness of the drug dose ordered for a specified infant. Experienced nurses tended to be more certain, although wrong, in their judgment when compared to inexperienced nurses. Eleven pediatricians, when given the same test, scored higher than the nurses but still made errors at the rate of one of every 26 computations attempted. Five registered pharmacists who were tested demonstrated far better computational skills than either the nursing or physician group.