New information on cardiopulmonary bypass continues to be produced by investigators from many disciplines. Investigations are related to problems and complications resulting from use of the heart-lung machine. The relationship of perfusion and pressure during bypass in brain, kidney, and other organs is the subject of several reports. The studies confirm that low flow and pressure are safe with hemodilution and hypothermia. Investigations related to the pH stat and alpha stat blood gas schemes are sometimes inconclusive, but significant observations favor the use of the alpha stat blood gas scheme. The complications of choreoathetosis in pediatric patients appears to be related to low levels of hypothermia. Studies continue to show the many adverse effects of cardiopulmonary bypass on platelets, leukocytes, and the complement system. The minimum acceptable activated clotting time during cardiopulmonary bypass may be less than 400 seconds. Other authors address the complications of protamine infusion and heparin-induced thrombocytopenia.