Generalized aggressive periodontitis (GAgP) is an inflammatory condition resulting in destruction of tooth-supporting tissues. We examined the production of IL-1beta, IL-6, tumour necrosis factor (TNF)-alpha, IL-12 and IL-10 in cultures of peripheral mononuclear cells (MNC) from 10 patients with GAgP and 10 controls stimulated with periodontal pathogens or a control antigen, tetanus toxoid (TT) in the presence of autologous serum. The pathogens used were Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum, either as type strains or bacteria isolated from the participants' inherent oral flora. The P. gingivalis -induced production of IL-6 was approximately 2.5-fold higher in patients with GAgP than in healthy controls (P <0.05), while the corresponding TNF-alpha production was non-significantly elevated. IL-1beta production induced by P. gingivalis, as all cytokine responses induced by Pr. intermedia, F. nucleatum and TT was similar in the two groups. A reduced IL-12p70 response to Pr. intermedia and F. nucleatum was observed in smokers compared to non-smoking patients (P <0.02). To assess the role of serum factors in the elevated IL-6 response to P. gingivalis, MNC from two donors free of disease were stimulated with this bacterium in the presence of the various patient and control sera. An elevated IL-6 and TNF-alpha response was observed in the presence of patient sera (P <0.01 and P <0.04, respectively). The data suggest that an exaggerated production of IL-6 occurs in GAgP, and that pro-inflammatory serum factors play an essential role in the response.