The involvement of inflammation in the development and propagation of chronic subdural haematoma (CSH) was investigated by measuring the levels of inflammatory cytokines (tumour necrosis factor [TNF] alpha, interleukin [IL]-1 beta, IL-6, and IL-8). Peripheral venous blood and subdural fluid were obtained at the time of burr hole surgery from 34 patients with CSH and from 9 with subdural effusion. The levels of the inflammatory cytokines were analysed by enzyme-linked immunosorbent assay. The blood levels of TNF alpha, IL-1 beta, IL-6, and IL-8 in both CSH and subdural effusion groups were almost within the range of normal subjects, and no differences were observed between the two groups. IL-6 and IL-8 in the subdural fluid were much higher than in the blood of both groups, and the levels in CSH patients were significantly higher (10 times) than in subdural effusion patients. Local elevation of inflammatory cytokines in the subdural space of both CSH and subdural effusion without systemic change suggests the presence of local inflammation in the two diseases. The same behavioural patterns of cytokines for these and higher levels of cytokines in the CSH also suggest that inflammatory cytokines may be involved in the continuous development from subdural effusion to CSH and propagation of CSH.