T cells have been identified as key players in the pathogenesis of type 1 diabetes. However, the exact role of T-cell subpopulations in this pathway is presently unknown. The purpose of this study was to assess the expression pattern of two lineage-specifying transcription factors GATA-3 and T-bet, which are important in T helper type 1 (Th1) and Th2 cell development, respectively. Gene expression analysis of peripheral blood mononuclear cells (PBMCs) was performed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Plasma levels of IFN-γ and IL-4 were also determined by ELISA. T-bet and IFN-γ gene expression was significantly lower in patients group compared with healthy controls (p<0.05). The expression of GATA-3 was relatively similar in patients and controls; however, IL-4 mRNAs were significantly increased in the PBMCs from patients as compared with normal controls (p<0.05). In addition, a marked increase in plasma IL-4 levels were observed in patient group compared with controls (p<0.001). To the contrary, IFN-γ protein levels were decreased in patients in comparison with controls (p<0.001). These data suggest additional implications of the role of Th1/Th2 imbalance for the immunopathogenesis of type 1 diabetes.