A model of the proximal nephrovascular unit is formulated which tracks the concentrations and fluxes of Na+,K+,H+, Cl-, HCO;, HPOi, H2P0;,
glucose, and urea. In this model, a glomerulus provides initial data for proximal tubule and peritubular capillary, which exchange mass across a wellstirred interstitial compartment. The equations for glomerular and peritubular capillaries include the hemoglobin buffer model of Atherton et al. (1984). The glomerulus itself constitutes a boundary value problem, with Bowman's space concentrations determined by the integral of transported solute. The glomerular problem is solved in two steps ---first, the determination of protein concentration and volume flow, and then the calculation of the concentrations of the permeant solutes. In the calculation of the permeants, it is found that if only total filtration rates are required, the assumption of Donnan equilibrium at the glomerular capillary end is a useful approximation, which permits substantial savings in computation time. This model nephron is the first to allow simulation of physiologic maneuvers in which both tubular and peritubular conditions may vary simultaneously, such as changes in renal perfusion pressure, afferent or efferent arteriolar resistance, or plasma protein concentration.