Cytokine responses to surgical trauma have been studied in 70 patients undergoing various neurosurgical procedures. Serum concentrations of interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), interleukin-8, (IL-8), tumour necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) were measured before and after surgery using enzyme-linked immunosorbent assays. The serum concentrations of IL-1 beta, IL-8, TNF-alpha, and IFN-gamma did not change significantly following neurosurgical operations. In contrast, serum IL-6 levels were significantly elevated following surgery, peaking at postoperative day 1 and then gradually decreasing. Maximum IL-6 concentrations were considerably higher in patients who underwent surgery for brain tumours or aneurysms as compared with patients who had a ventriculoperitoneal shunt, neurovascular decompression or transsphenoidal adenomectomy. Intra-operative use of methylprednisolone, which is known to block the production and action of cytokines, suppressed the increase in IL-6 levels after surgery. There was a statistically significant correlation between the IL-6 peak concentration and the length of surgery in patients not treated with steroids, but not in patients treated with steroids. Additionally patients who underwent supratentorial surgery had higher peak concentrations of IL-6 than those who underwent infratentorial surgery. These results suggest that IL-6 is an early marker of tissue damage and may be useful in assessing the extent of postoperative stress.