Interleukin-1 receptor antagonist (IL-1Ra) is a specific inhibitor of interleukin-1 (IL-1). It is structurally similar to IL-1 and binds to IL-1 cell surface receptors, but does not transduce a signal. To examine the relationship between the production of IL-1Ra and IL-1, we incubated peripheral blood mononuclear cells (PBMC) with endotoxin (10 ng/ml) and after 24 h measured the total synthesis (intra- and extracellular) of IL-1Ra, IL-lα and IL-1β. PBMC from 25 patients with chronic renal failure were studied. The total synthesis of IL-1Ra closely correlated with that of IL-1β (R = 0.786, p 0.05). These results suggest that in dialysis patients, the endogenous production of IL-1Ra is a ‘footprint’ of IL-1β production and can probably be used as a marker of the level of production of IL-1.