Recent evidence suggests that autoimmune animal diabetes is associated with an imbalance between the Th1 and Th2 arms of the cellular immune system. However, limited data is available regarding the Th1/Th2 imbalance in human Insulin dependent diabetes mellitus (IDDM) patients. Therefore, we examined the peak levels, secretory pattern and total cytokine production (calculated as the area under the curve, AUC) of the Th1 cytokines, IL-2 and IFN-γ, and Th2 cytokines, IL-4 and IL-10, from stimulated peripheral blood mononuclear cells, from 17 IDDM patients and 24 normal controls. In contrast to controls, diabetic patients were characterized by an early, uniformly low secretion of Th2 cytokines, followed by a late increased secretion of Th1 cytokines. This resulted in significant differences in secretory patterns of IFN-γIL-2, IL-4 and IL-10 between the two groups;P<0.001,P<0.005,P<0.005 andP<0.001, respectively. No correlation was found in the diabetic patients between any profiles of the cytokines and their various clinical parameters, including age, gender, disease duration, insulin requirements or glycated hemoglobin levels. In conclusion, our data provides the first comprehensive evidence for an independent and persistent impairment of both Th1 and Th2 cytokine secretory patterns in IDDM patients.