Renal mesangial cells are perivascular cells located within the central portion of the glomerular tuft between capillary loops. They constitute 30-40% of the total glomerular cell population. They regulate the intraglomerular capillary flow and ultrafiltration surface via mesangial cell contraction and release of growth factors and vasoactive agents. By pinocytosis and phagocytosis, mesangial cells remove local accumulation of macromolecules in the mesangial space. Mesangial cells also synthesize, assemble and control turnover of the mesangial matrix. Overproduction of mesangial cells occurs in various glomerular diseases; such as IgA nephropathy, mesangioproliferative glomerulonephritis, lupus nephritis, glomerulosclerosis and diabetic nephropathy. Such critical involvements suggest rat renal mesangial cells are an ideal model for studying mesangial injury and glomerular functions under both physiological and pathophysiological conditions.