This study investigated the mRNA expression of the platelet-derived growth factor (PDGF) A-chain and B-chain and PDGF-beta receptor in glomeruli of 15 immunoglobulin A (IgA) nephropathy kidneys and those with minimal-change lesion (N = 7), membranous nephropathy (N = 3), and focal segmental glomerulonephritis (N = 5), by using competitive RT-PCR methods. The level of PDGF B-chain and beta receptor mRNA expression in IgA nephropathy was significantly higher than in the other forms of glomerulonephritis, but mRNA expressions of PDGF A-chain were not significantly different. Significant correlations were observed between the urinary protein level and the mRNA level of PDGF-beta receptor expression and PDGF B-chain expression, and between the serum creatinine level and the mRNA level of PDGF-beta receptor expression. The PDGF B-chain and beta-receptor may be upregulated and accelerate cell proliferation in a paracrine or autocrine manner and may play a role in the pathogenesis of IgA nephropathy.