In a prospective study of 312 patients undergoing elective coronary bypass surgery we evaluated 50 preoperative, intraoperative and postoperative factors with the aim of identifying predisposing causes for perioperative neurological morbidity. Factors which showed a significant association with the development of neurological complications included the duration and severity of heart disease before surgery; the presence of extracoronary vascular disease; history of cardiac failure; history of diabetes; difficulty in terminating bypass; intraoperative mean arterial pressure levels of less than 40 mmHg; a large drop in haemoglobin level during surgery; prolonged stay in the intensive therapy unit after operation; and abnormalities of blood pressure control in the postoperative period. The significance of these findings is discussed and a comparison made with data available from previous studies.