Peritoneal macrophages from multiple autoimmune-prone strains of mice (MRL/lpr, MRL/+, NZB/W, BXSB, and B6/gld) show defective expression of the cytokines IL-1 and IL-6. Autoimmune mice were all used between 1 and 6 weeks of age, the earliest times being well before the onset of overt disease. Northern blot analysis reveals a parallel reduction in the levels of IL-1 alpha, IL-1 beta, and IL-6 mRNA. In contrast, the production of other proteins, including the cytokine TNF-alpha, appears to be normal. These findings imply an imbalance within the cytokine network of autoimmune macrophages. Studies on bone marrow-derived macrophage precursors, as well as macrophages from chimeric mice, suggest an intrinsic macrophage defect as opposed to conditioning by the autoimmune environment. This defect appears to be constant throughout the lifespan of autoimmune MRL/lpr mice, being equally apparent in 1-week old mice as in fully diseased 6-12-month-old mice. Aberrant regulation of IL-1 and IL-6 represents a novel defect in the function of autoimmune macrophages that is both intrinsic and substantial, and has the potential to contribute to the immune dysregulation that characterizes autoimmunity.