The aim of our study was to analyse the serum interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) levels in patients with AS and their relationship with disease activity. An ELISA test was used to analyse serum cytokine (IL-6, TNF-alpha, IL-1 beta and IFN-gamma) levels in 69 patients with AS. Results were compared with those from 43 patients with RA and 36 patients with non-inflammatory back pain. The relationship between serum concentrations of the different cytokines and parameters of disease activity and severity in AS patients was also evaluated. IL-6 and TNF-alpha serum levels, but not IL-1 beta and IFN-gamma, were significantly higher in AS than in NIBP. However, patients with RA showed higher serum levels of IL-6, TNF-alpha and IFN-gamma than both AS and NIBP patients. In AS, IL-6 correlated with clinical parameters of disease activity with significant correlation being observed with laboratory parameters of inflammation such as ESR, CRP, platelet count and clinical parameters of severity such as vertebral mobility. TNF-alpha did not correlate with laboratory or clinical parameters of activity. Macrophagic cytokines (TNF-alpha and IL-6), are increased in AS patients and IL-6 closely correlated with the activity of the disease.