Although it has been demonstrated that both surgery and anaesthesia induce immune suppression, it remains unclear whether there are differences between anaesthetic techniques in inducing immune suppression in cancer patients. The aim of this present study was to compare the effects of total intravenous anaesthesia (TIVA) and isoflurane anaesthesia on plasma concentrations of interleukins IL-6 and IL-10 in patients undergoing surgery for colorectal cancer. A randomised, controlled, open-label study. University hospital. Seventy patients undergoing open colorectal surgery with tumour resection were randomised prospectively into one of two groups; 60 patients completed the study. Group 1 (n = 30) received TIVA and group 2 (n = 30) received isoflurane. Propofol infusion rate and inspired concentration of isoflurane were titrated to achieve bispectral index values of 40 to 55. Plasma concentrations of IL-6 and IL-10 were measured preoperatively, before surgical incision and at 2 and 24 h postoperatively. The area under the curve (AUC) for IL-6 and IL-10 over 24 h and plasma interleukin concentrations at each time point were compared between the groups. Median (range) AUC for IL-6 was 4657 (1219 to 8427) pg h ml in the TIVA group and 5349 (839 to 8126) pg h ml in the isoflurane group. For IL-10, AUC was 1165 (344 to 5258) pg h ml in the TIVA group and 1405 (463 to 8161) pg h ml in the isoflurane group. When comparing interleukin concentrations between study groups at different time intervals, there were no significant differences in plasma concentrations of IL-6 or IL-10. Intragroup comparisons revealed that IL-6 and IL-10 concentrations were significantly increased 2 and 24 h postoperatively in both groups when compared with their baseline values (P < 0.01 and P < 0.01 at 2 and 24 h for the TIVA group and isoflurane group, respectively). We found no significant differences between the effects of TIVA and isoflurane anaesthesia on plasma concentrations of IL-6 and IL-10 after colorectal cancer surgery during the first 24 h postoperatively. Further studies are needed to determine differences in long-term outcome of these patients. Clinicaltrials.gov identifier: NCT01902849. The study was registered retrospectively.