BACKGROUND Pro-inflammatory cytokines like interleukin (IL)-1 beta and tumor necrosis factor-alpha (TANF-alpha) are believed to play a significant role in dialysis-related morbidity. It has been previously demonstrated that the endogenous synthesis of interleukin-1 receptor antagonist (IL-1Ra) is a reliable marker of the level of IL-1 beta synthesis in hemodialysis (HD) patients. In this study, we assessed the impact of clinical and laboratory variables on IL-1Ra synthesis by peripheral blood mononuclear cells (PBMC) in patients on HD with unsubstituted cellulose dialyzers. METHODS IL-1Ra by PBMC was measured by a specific non-cross-reactive radioimmunoassay. Day to day variation in cytokine synthesis, the correlation between cytokine synthesis under different in vitro stimulatory conditions, and the influence of clinical and laboratory variables on cytokine synthesis were studied. RESULTS Although there was a trend towards greater IL-1Ra synthesis by unstimulated, endotoxin-stimulated and IgG-stimulated PBMC drawn before the second and third dialysis sessions of the week when compared to the first dialysis treatment, this was not statistically significant. There was a strong correlation between IL-1Ra synthesis by PBMC cultured under different stimulatory conditions that was best observed between IL-1Ra cell content and from endotoxin-stimulated PBMC (r = 0.51, P = 0.0001), and endotoxin- and IgG-stimulated PBMC (r = 0.44, P = 0.0001). In addition, there was a close correlation between total synthesis (cell associated and secreted) and secreted levels of IL-1Ra in unstimulated (r = 0.59, P = 0.0001) and endotoxin-stimulated PBMC (r = 0.69, P = 0.0001). Interestingly, there was an inverse correlation between IL-1Ra synthesis and duration of dialysis that was strongest for secreted IL-1Ra from unstimulated (r = -0.50, P = 0.002) and endotoxin-stimulated PBMC (r = -0.34, P = 0.04). There was no significant correlation between IL-1Ra synthesis by PBMC and other clinical and laboratory indices. CONCLUSIONS The observations from this study indicate that: (1) in HD patients, there were no significant differences in cytokine synthesis by PBMC drawn before the three different dialysis treatments during the week; (2) there is a close relationship between IL-1Ra synthesis from PBMC cultured under different stimulatory conditions; (3) the secreted levels of IL-1Ra correlate directly with total synthesis (cell-associated and secreted); (4) with the exception of duration of dialysis, none of the other clinical or laboratory parameters correlated with cytokine synthesis; and (5) the diminished endotoxin- or IgG-stimulated IL-1Ra synthesis with increasing time on dialysis is possibly another sign of the impaired host-defense system in patients on long-term hemodialysis.