It has been suggested that large doses of opioids may suppress the interleukin-6 response to surgery. We examined the effects of the supplementation of inhalational anaesthesia with either 3 or 15 micrograms.kg-1 fentanyl on the circulating interleukin-6, interleukin-8, C-reactive protein, cortisol and glucose concentrations in 16 patients undergoing pelvic surgery. In both groups, surgery evoked the expected glucose, cortisol and interleukin-6 response but no increase in interleukin-8 was detected. There were no significant differences between the two groups. We conclude that the supplementation of inhalational anaesthesia with conventional doses of opioids does not modify the cytokine response to surgery.