The influence of surgical stress on haemodynamics during neurolept anaesthesia (NLA) was studied in ten patients, while they were awake, under anaesthesia prior to surgery and peroperatively. Systemic arterial, pulmonary arterial, right atrial and pulmonary capillary wedge pressures, as well as cardiac ouput (Qt), arterial oxygen content and mixed venous oxygen content, were measured. Systemic and pulmonary vascular resistances, arterial-venous oxygen content difference (AVD), oxygen consumption (VO2) and cardiac index (CI) were calculated. On institution of anaesthesia, CI fell from 2.8 +/- 0.1 1/min-m2 to 2.5 +/- 0.2 1/min-m2 and systolic arterial pressure (SBP) fell from 13.4 +/- 0.5 kPa to 10.2 +/- 0.3 kPa. During surgery CI rose to 3.3 +/- 0.1 1/min-m2 and SBP rose to 15.7 +/- 0.6 kPa. Prior to anaesthesia, AVD was 40.2 +/- 0.2 ml/l. Under anaesthesia prior to surgery, AVD did not change, but VO2 declined from 207 +/- 13ml/min to 171 +/- 10 ml/min. During surgery, AVD fell to 30.5 +/- 0.3 ml/l, while VO2 remained unchanged. It is concluded that NLA has a direct metabolic depressant effect and, in association with surgery, is accompanied by hyperkinetic circulation.