In current study, the expressions of protein kinase C (PKC)-alpha, beta I and beta II as well as their correlation to the expression of transforming growth factor-beta I (TGF-beta I) and vascular endothelial growth factor (VEGF) were investigated in glomeruli of normal renal tissues taken from human kidney tumors and kidney tissues from patients with diabetic nephropathy (DN). The accumulation of glomerular extracellular matrix (ECM) was determined by PAS staining, the expressions of PKC-a, PKC-beta I, PKC-beta II, TGF-beta I and VEGF were measured by semi-quantitative immunohistochemistry. Our results showed that in glomeruli of normal renal tissues, PKC-alpha and beta II had a strong expression whereas the expression of PKC-beta I was weak; in glomeruli of DN patients, the expressions of PKC-alpha, PKC-beta I, VEGF and TGF-beta I and the accumulation of ECM increased significantly, but the expression of PKC-beta II decreased markedly. Meanwhile, the expressions of PKC-alpha and beta I had a positive correlation to the expressions of VEGF and TGF-beta I respectively, whereas PKC-beta II showed no correlation to VEGF and TGF-beta I. It is concluded that the expressions of PKC-alpha, beta I and beta II in glomeruli of normal subjects and DN patients are different. PKC-alpha seems to play a critical role in human DN by up-regulating VEGF expression, whereas PKC-beta I is relatively important for the up-regulation of TGF-beta I and the accumulation of ECM under diabetic conditions.