Recent evidence suggests that the balance between serine proteases and their inhibitors is central to the maintenance of the glomerular extracellular matrix. We have characterised the urokinase type and the tissue type plasminogen activators (PA) and their inhibitor, PAI-1, secreted from glomerular epithelial and mesangial cells as well as their co-cultures and have investigated the effect of transforming growth factor-beta 1 (TGF-beta 1) on the production of such species. Similar data were derived from whole glomeruli suspensions. TGF-beta 1 increased PAI-1 production significantly in epithelial and mesangial cells as well as in whole glomeruli, while PA production was decreased; platelet-derived growth factor had no effect. These effects are consistent with a possible decrease in matrix proteolysis, suggesting a mechanism by which TGF-beta 1 may enhance mesangial matrix accumulation, a characteristic of many forms of glomerular disease.