Cytokines are believed to play an important role in the pathogenesis of periodontal diseases. In the present study, gingival crevicular fluid (GCF) levels of two important cytokines, interleukin 1-beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha) and, in addition, serum IL-1 beta levels, were determined in patients with severe and rapid periodontal breakdown by use of ELISA. While IL-1 beta was detected in all of the GCF samples studied, TNF-alpha could only be detected in about half the samples, The mean GCF IL-1 beta level was 38.45 +/- 13.99 pg/mL, and the mean TNF-alpha level was 3.20 +/- 1.39 pg/mL, respectively. The GCF IL-1 beta levels also presented a strong positive correlation with the mean pocket depths. Although weak, both of the cytokines also presented correlations with the presence of bleeding on probing. Additionally GCF samples contained increased IL-1 beta levels when compared with the serum samples suggesting local production mechanisms. The findings of the present study suggest that these cytokines may be involved in the pathogenesis of periodontal diseases (IL-1 beta being more significant), and also may help in defining the active phase of periodontal breakdown.