DEEN, WM, CR ROBERTSON, AND BM BRENNER. A model of glomerular ultrajltration in the rat. Am. J. Physiol. 223 (5): 1178-l 183. 1972.-A mathematical model has been developed to investigate the influence of a number of physiological variables on the net driving pressure for ultrafiltration(PuF) in the rat glomerulus. The model was used to predict osmotic pressure differences as functions of distance along a glomerular capillary for a wide range of glomerular capillary plasma flow rates, membrane hydraulic permeabilities(k), and axial pressure drops; and these pressure profiles are consistent with recently reported experimental findings. When filtration pressure equilibrium is achieved, results obtained with the model indicate that estimates of PUF at the beginning and end of the glomerular capillary bed cannot be used to infer the correct magnitudes of the mean value of PUF or k in the normal rat. The results also indicate that changes in single-nephron glomerular filtration rate will vary in proportion to changes in plasma flow rate when filtration pressure equilibrium occurs. glomerular filtration rate; intrarenal plasma flow; colloid osmotic pressure; computer simulation; glomerular pressure