Glomerular capillaries are perfused at a high hydraulic pressure. Since the capillary mesangium interface presents no morphologically apparent pressure barrier, it is suggested that the hydraulic pressure in the mesangium may also be high. This paper analyzes the structures in the glomerular tuft that are capable of counteracting the distending forces exerted on the tuft by the high hydraulic pressure in its center. The skeletal element of the glomerular tuft is the glomerular basement membrane (GBM). The combination of the GBM with the contractile apparatus of mesangial cells represents the main system stabilizing the glomerular tuft. The mesangial cell-GBM connections counteracting the expansion of glomerular capillaries appear less susceptible to injury than those counteracting mesangial expansion.