Oesophageal Doppler monitoring allows non-invasive estimation of stroke volume and cardiac output. We studied the impact of Doppler guided fluid optimisation on haemodynamic parameters, peri-operative morbidity and hospital stay in patients undergoing major bowel surgery. Fifty-seven patients were randomly assigned to Doppler (D) or control (C) groups. All patients received intra-operative fluid therapy at the discretion of the non-investigating anaesthetist. In addition, Group D were given fluid challenges (3 ml x kg(-1)) guided by oesophageal Doppler. Group D received significantly more intra-operative colloid than Group C (mean 28 (SD 16) vs. 19.4 (SD 14.7) ml x kg(-1), p = 0.02). Cardiac output increased significantly for Group D whilst that of controls remained unchanged. The mean difference between the groups in final cardiac output was 0.87 l x min(-1) (95% confidence interval 0.31-1.43 l x min(-1), p = 0.003). Five control patients required postoperative critical care admission. Fluid titration using oesophageal Doppler during bowel surgery can improve haemodynamic parameters and may reduce critical care admissions postoperatively.