Hyaluronan (HA) is a ubiquitous connective tissue glycosaminoglycan component of most extracellular matrices and alterations in its synthesis have been suggested to be involved in the glomerular changes of diabetic nephropathy. Similarly it has been suggested that macrophages are involved in the initiation of diabetic glomerular injury. Much less is known regarding the role of the prognostic value of changes in interstitial HA and interstitial inflammatory infiltrate. The aim of this study was to examine the potential association of inflammatory infiltrate, deposition of the matrix component hyaluronan and inter-alpha inhibitor (which is involved in HA assembly) and clinical outcome in diabetic nephropathy. Histological specimens of 40 patients with biopsy proven diabetic nephropathy were examined. Based on the rate of change in estimated GFR (eGFR, abbreviated MDRD formula), patients were defined as late presenters, progressors or non-progressors. The degree of interstitial fibrosis was associated with progression of disease and late presentation. There was a significant greater number of CD68-positive cells in the interstitium of patients who subsequently developed progressive renal disease, or those who presented with advanced disease compared to non-progressors. In contrast, there was significant staining for interstitial HA in all the patient groups. Furthermore there was no correlation between the accumulation of HA and CD68-positive macrophages. In addition all patients with biopsy-proven diabetic nephropathy had significantly greater interstitial IalphaI compared to the normal controls and there was a significant correlation between interstitial HA and IalphaI. Increased HA is seen at all stages of diabetic change in the kidney but is not predictive of progression. Macrophage influx, however, is directly related to the progression of diabetic nephropathy and is not associated with HA accumulation.