The aim of this study was to determine the relationship between histological, immunohistochemical (IHC) and biological data in the assessment of interstitial fibrosis in patients with glomerular diseases. A group of 41 patients with primary and secondary glomerulonephritis was studied. In order to quantify the histological changes and to assess the extent of active-inflammatory and chronic-sclerotic/fibrotic interstitial lesions, we adapted a scoring system, initially used for lupus nephritis, and ANCA-associated vasculitis. IHC labeling procedures with monoclonal antibodies anti-smooth muscle actin (SMA), anti-vimentin and anti-transforming growth factor beta (TGFbeta) were assessed using a semi-quantitative score, correlated with the histological and biological data. Our results showed that interstitial labeling of SMA correlated with scores for sclerotic/fibrotic lesions (chronicity index) and with active-inflammatory lesions (interstitial infiltrate, activity index). Interstitial vimentin correlated with the score for interstitial infiltrate. Both interstitial vimentin and TGFbeta immunopositivity correlated with sclerotic/fibrotic lesions (interstitial fibrosis, tubular atrophies, vascular hyalinosis/fibrosis, chronicity index), and negatively with glomerular filtration rate. An important correlation was found between the interstitial labeling of the two IHC markers of myofibroblasts (SMA and vimentin). We conclude that IHC studies related to clinico-biological and histological data can have an important role in the evaluation of the glomerular diseases, but the classical histological investigation assessed through quantification has still not lost its importance.