In situ hybridization, immunohistochemistry, and TUNEL staining were applied to renal biopsy specimens of immunoglobulin A nephropathy (IgAN) patients to determine the expression of nitric oxide synthase (iNOS) (mRNA and protein), p53, and their potential roles in renal cell apoptosis in relation to the development of pathologic lesions. Fifty-one cases were categorized into four subgroups (A-D) according to the presence of progressive histopathological features. A cell type-specific and differential overexpression of iNOS mRNA and protein was demonstrated in glomerular cells in subgroups (A-C) and was found to correlate well with the upregulation of p53 protein by glomerular endothelium and epithelium in early- and advanced-stage disease. In the tubulointerstitium, induction of iNOS products was evident in damaged tubules in late-stage disease, in parallel with the upregulation of p53 protein levels in these tubules. Increased TUNEL staining observed in glomeruli with progressive lesions and tubules with degenerative changes positively correlated with the expression levels of iNOS and p53 in glomerular endothelium, epithelium, and their overexpression in damaged tubules. Clinicopathologic correlations demonstrated that induction of iNOS products in renal cells was associated with indices of poor renal prognosis in human IgAN. The coupled induction of iNOS and p53 upregulation in intrinsic renal cells of IgAN may be linked with both pro- and anti-apoptotic activities, thus playing an important role in mediating progressive renal injury and determining renal outcome in human IgAN.