The compensatory haemodynamic response to acute isovolaemic haemodilution in elderly patients is controversial. In awake patients a significant increase in cardiac output was described [1], whereas in anaesthetized patients no increase in cardiac output was observed [2]. Thirteen patients, 65 years of age or older, scheduled for intraabdominal surgery were studied. Exclusion criteria were: history of coronary artery disease or congestive heart failure. Anaesthesia was induced with midazolam (50-120 μg kg−1), fentanyl (3-10 μg kg−1) and pancuronium (0.12 mg kg−1) and maintained with midazolam (0.75 μg kg−1 min−1) and fentanyl (0.05 μg kg−1 min−1) infusions. Measured variables were: mean (pulmonary) arterial (M(P)AP), central venous (CVP) and pulmonary capillary wedge pressures (PCWP), heart rate (HR), cardiac index (CI, thermodilution), arterial and mixed venous blood gases, haemoglobin concentration and ST segment deviation in leads II and V5. The above measurements were performed at baseline, after 6 mL kg−1 and after 12 mL kg−1 haemodilution (isovolaemic exchange of blood with 6% hydroxyaethyl starch). Responses to haemodilution were analysed by means of a repeated measures Anova (P<0.05). Data are presented as means±SEM. The mean age of the patients was 73±2 years. During haemodilution haemoglobin decreased from 12.2±0.5 gm dL−1 to 9.3±0.4 gm dL−1. CVP and PCWP were stable at 5 mm Hg. CI (Fig. 1a) and oxygen (O2) extraction (Fig. 1b) increased during haemodilution resulting in a stable O2 consumption (V˙O2I) (Fig. 1c). AVDO2 decreased during haemodilution. MAP, MPAP and ST segment deviation in leads II and V5 were unchanged during haemodilution (Fig. d).Fig. 1: (abstract 2). Changes (a) in cardiac index (b) oxygen extraction (c) oxygen consumption index (d) and ST segment deviation.* sign. change (P<0.05) during haemodilution.Moderate isovolaemic haemodilution to a haemoglobin value of approximately 9 gm dL−1 was well tolerated by elderly patients anaesthetized with midazolam and fentanyl infusions. The compensatory response to maintain whole body O2 consumption consisted in an increase of both, cardiac output and O2 extraction. This is in contrast to the response pattern of elderly patients anaesthetised with a neuroleptic analgesic technique, where only an increase in O2, extraction but no increase in cardiac output was observed during haemodilution [2]. The anaesthesia technique thus might modulate the compensatory response mechanisms during haemodilution.