Cytokines are involved in the pathogenesis of type 1 diabetes. The disease is characterized by T cell-mediated beta cell destruction and a biased Th1 cytokine pattern. Type 2 diabetes also presents an inflammatory cytokine imbalance. In this study, mRNA expression of cytokines IL-12, TNF-alpha, IL-1, and IL-6 was studied in monocytes from diabetic patients after in vitro immune stimulation. Whereas IL-12(p40) was highly expressed in type 1 diabetic patients, TNF-alpha, IL-1, and IL-6 transcripts were elevated in type 1 but especially type 2 diabetic patients compared with healthy controls, suggesting an important proinflammatory milieu. We conclude that circulating monocytes from type 1 as well as type 2 diabetic patients have an aberrant cytokine profile when stimulated by an immune stimulus such as IFNgamma. This condition not only is likely to be involved in disease pathogenesis, but may contribute to its later complications.