Expansion of the glomerular mesangial matrix (MM), thickening of the glomerular basement membrane (GBM), and eventually the development of glomerulosclerosis are often seen in immunologically mediated kidney diseases. In addition to quantitative changes in the extracellular matrix (ECM), qualitative changes in ECM molecules may contribute to alterations in the composition of the glomerular matrix. The expression of collagen IV, alpha 1-5(IV) mRNA, and polypeptides was therefore investigated during the development of chronic graft-versus-host disease (GvHD) in mice, a model for lupus nephritis, and in chronic serum sickness (CSS) in rats, a model for membranous nephropathy. Immunohistochemical studies showed increased mesangial expression of alpha 1 and alpha 2 early in the disease, but only late in the GBM. In contrast, alpha 3 and alpha 4 increased in the GBM during disease, but not in the MM. The mRNA levels for all collagen IV chains were increased in isolated glomeruli before morphological alterations were detectable. The mRNA increase was earlier and more profound for alpha 3, alpha 4 and alpha 5 than for alpha 1 and alpha 2. Expression of alpha 3(IV) was greatest in GvHD, whereas expression of alpha 4 was greatest in CSS. As determined by in situ hybridization (ISH), alpha 1 mRNA was observed dispersed in the glomerulus, but alpha 3, alpha 4, and alpha 5 mRNAs were mainly located in cells at the periphery of the glomerular tuft. The changes in the relative abundance of collagen IV mRNA in disease states may perturb the collagen IV network, altering glomerular structure and function, and may thereby play a central role in the development of glomerulonephritis and glomerulosclerosis.