Cardiopulmonary bypass (CPB) and hypothermic circulatory arrest induce leukocyte and platelet activation and cytokine production as part of the inflammatory response to bypass. These events are thought to be responsible for producing at least some of the morbidity of bypass. We studied the effects of a monoclonal antibody to a specific leukocyte adhesion integrin, CD18, on the deleterious effects of CPB and circulatory arrest in piglets using techniques from infant heart surgery. Seventeen immature piglets were subjected to CPB, cooling, 1 hour of circulatory arrest at 15 degrees C, and subsequent reperfusion and rewarming. Nine piglets received anti-CD18 monoclonal antibody (group MAb), and eight randomly selected control piglets received none (group C). Monoclonal antibody to leukocyte integrin CD18 significantly decreased deleterious effects of CPB and hypothermic circulatory arrest in our immature animal model. This study suggests that antiadhesion therapy that alters fundamental leukocyte/endothelial interactions during open heart surgery may be protective against some deleterious effects of bypass and circulatory arrest in infants.