Studies have shown that high levels of glucose and angiotensin II (Ang II) stimulate hypertrophy and the expression of matrix protein genes in mouse proximal tubular cells in vitro. The present study tested the hypothesis that blockade of the renin-angiotensin system (RAS) inhibits the stimulatory effect of high levels of glucose on the expression of the renal angiotensinogen (ANG) gene and the formation of Ang II and subsequently attenuates the induction of hypertrophy in kidney proximal tubular cells. Immortalized rat proximal tubular cells (IRPTC) were cultured in monolayer. The levels of expression of rat ANG and ANG mRNA in the IRPTC were quantified by specific radioimmunoassays for rat ANG (RIA-rANG) and by a reverse-transcription polymerase chain reaction (RT-PCR) assay, respectively. Hypertrophy of IRPTC was analyzed by flow cytometry (FACScan) and cellular protein assay. Our studies showed that losartan (an Ang II (AT1)-receptor blocker), perindopril and captopril (inhibitors of angiotensin-converting enzyme) blocked the stimulatory effect of a high level of glucose (i.e. 25 mM) on the expression of the rat ANG gene and hypertrophy in IRPTC but not by the Ang II (AT2)-receptor blocker. Our studies indicate that the blockade of RAS is effective in inhibiting the stimulatory effect of hyperglycemia on the expression of the ANG gene and hypertrophy in IRPTC, supporting the notion that the local formation of intrarenal Ang II may play a role in the development of renal hypertrophy during early diabetes.