A mathematical model of the renal corpuscle is presented and used to quantify the effect on filtration rate, nephron blood flow and hydrostatic pressure in the glomerular capillaries of variations in: 1. the hydrostatic pressure in Bowman's space; 2. the hydrodynamic resistances of the afferent and efferent arterioles; 3. the ultrafiltration coefficient of the glomerular membrane; 4. the hydrostatic pressure in the peritubular capillaries; 5. the arterial haematocrit and plasma protein concentration. The model is derived from the principle of conservation of mass and volume. Hydrostatic pressure gradients along the glomerular capillaries are neglectec. The hydrodynamic resistances of the afferent and efferent arterioles are assumed to be determined by two independent factors, one being determined by the vascular dimensions, the other by the haematocrit. Blood flow is considered to be related in a linear manner to the hydrostatic pressure decreases along these vessels. The effect of changing the hydrostatic pressure in Bowman's space on nephronGFR was calculated and found to agree with experimental measurements. When corpuscular hydrodynamics are related to variations in the hydrodynamic resistance of the afferent or efferent arteriole it is seen that the change in efferent arteriolar plasma flow accompanying altered nephronGFR is very sensitive to the way in which the change is produced. In contrast changes in glomerular capillary pressure and filtration fraction are insensitive. The calculations indicate that differences measured in nephronGFR between superficial and juxtamedullary nephrons can be explained by assuming that the diameters of the afferent and efferent arterioles of the juxtamedullary nephrons increase in direct proportion to the diameter of the renal corpuscle.