The synovial fluid (SF) of rheumatoid arthritis (RA) patients contains a mixture of inflammatory mediators. In order to determine whether certain cytokine patterns locally in the joint are specifically related to the chronic inflammation in RA, the concentrations of interleukin (IL)-1alpha, IL-1beta, IL-6, IL-10, transforming growth factor-beta (TGF-beta), tumour necrosis factor-alpha (TNF-alpha) and IgG2b-inducing factor (IgG2bIF) were measured in SF from 22 patients with RA and 22 patients with other types of arthritic lesions. High levels of IL-10, latent and active TGF-beta and the presence of IgG2bIF are significantly correlated with RA when corrected for age. As these factors have the capacity to promote antibody production, they might contribute to the maintenance of local antibody production in RA synovial tissues. All RA-SF samples contained detectable levels of IL-10 and all except one contained IL-1beta, while concentrations in several non-RA-SF samples were below detection limits. IL-6 and TGF-beta were present in all SF samples from both RA and non-RA patients. The presence of IgG2bIF was strongly correlated with high levels of IL-10 and IL-1beta in SF. However, no distinct cytokine profile specific for the chronic inflammation characteristic of RA was found.