TGF-beta 1 is involved in the pathogenesis of glomerular sclerosis. We studied the intraglomerular expression of TGF-beta 1 mRNA in patients with glomerulonephritis using competitive polymerase chain reaction (PCR). This method is sensitive enough to quantify cDNA copies of mRNA present in small amounts of samples. Renal biopsy specimens were obtained from 42 patients with various kinds of glomerulonephritis. Ten glomeruli were dissected from renal biopsy specimens. Normal glomeruli were also obtained from the resected kidneys of eight patients with renal cell cancer. Total RNA was extracted from the glomeruli and reverse transcribed into cDNA with reverse transcriptase. To prepare samples containing identical amounts of beta-actin cDNA (8 pg), we performed competitive PCR by co-amplifying mutant templates of beta-actin with a unique EcoRI site. Next, to measure TGF-beta 1 cDNA, we performed competitive PCR by co-amplifying mutant templates of TGF-beta 1. We observed a higher glomerular expression of TGF-beta 1 mRNA in cases of mesangial proliferative glomerulonephritis having a moderate increase in mesangial matrix, diabetic nephropathy and diffuse proliferative lupus nephritis, compared with normal glomeruli. Results suggest that the intraglomerular synthesis of TGF-beta 1 may be involved in the progression of glomerulonephritis in humans.