In Reply.—We would like to thank Drs Welch and Byrne for their comments. We agree that the true incidence of persistent cerebral changes after cardiopulmonary bypass may be lower than our report suggests. Nevertheless, ventriculomegaly and dilatation of the subarachnoid spaces must remain a concern as we continue to operate on smaller and smaller children with increasingly complex lesions. Although these seem to be transient findings, as pediatricians we are frequently reminded of the subtle changes that occur in children's behavior and performance in much later stages of their lives. Additionally, we are concerned that prolonged cardiopulmonary bypass with the attendant problems with cerebral water may seem transient but may have more prolonged effects. Certainly, we cannot exclude the alternative possibility or perhaps the additional possibility that there is transient intracranial venous hypertension.