Glomerular mesangial cells are involved in a number of renal diseases and their response to glomerular hyperfiltration appears to be the final common pathway for progression of renal failure of diverse etiology. It is the mesangial cell which, in response to various mediators, proliferates and increases synthesis of mesangial cell matrix. This may result in the destruction of the glomerular space and may lead to end-stage renal failure. The main aim of this study was, therefore, to produce monoclonal antibodies to human mesangial cells, allowing better characterisation of these cells. Human glomerular cell cultures were successfully established, and pure mesangial cells obtained, these were used to immunise mice. Using standard hybridoma techniques, as well as the development of a novel mesangial cell micro-ELISA allowed the production of 29 antibodies to human glomerular mesangial cells. These antibodies showed minimal reactivity against normal and neoplastic leucocytes but had a greater reactivity with adherent cell lines. Fourteen out of 18 'acetone fast' antibodies were found to react with various cells and structures on normal kidney, six out of 14 of these reacted with mesangial cells on kidney sections. One of these monoclonal antibodies (F2.18) was characterised in more detail. Evidence from biochemical, immunochemical and functional studies revealed that this antibody was binding to a common determinant on the 1 and 2 chains of the VLA-1 family of cell surface matrix receptors. This is the first description of a monoclonal with such reactivity. Finally, the distribution of the different chains of the VLA-1 family was studied both on cultured glomerular mesangial and epithelial cells as well as on normal kidney sections. This is the first report of the production of monoclonal antibodies to purified glomerular mesangial cells. It is hoped that further characterisation of these antibodies will provide useful reagents for the study of the role of glomerular mesangial cells in the pathogensis of glomerulonephritis.