This study describes a high-throughput fluorescence dilution technique to measure the albumin reflection coefficient (Alb) of isolated glomeruli. Rats were injected with fluorescein isothiocyanate-dextran 250 (75 mg/kg) and the glomeruli were isolated in a 6% bovine serum albumin solution. Changes in the fluorescence of the glomerulus due to water influx in response to an imposed oncotic gradient was used to determine Alb. Adjustment of the albumin concentration of the bath from 6% to 5%, 4%, 3%, and 2 % produced a 10%, 25%, 35%, and 50% decrease in the fluorescence of the glomeruli. Pretreatment of glomeruli with protamine sulfate (2 mg/ml) or TGF-β1 (10 ng/ml) decreased Alb from 1 to 0.54 and 0.48, respectively. Water and solute movement were modeled using the Kedem-Katchalsky equations and the measured responses closely fit the predicted behavior, indicating that loss of albumin by solvent drag or diffusion is negligible in comparison to the movement of water. We also found that Alb was reduced by 17% in Fawn Hooded Hypertensive rats, 33% in hypertensive Dahl Salt-sensitive (SS) rats, 26% in streptozotocin-treated diabetic Dahl SS rats and 21% in 6 month old Type II diabetic nephropathy rats relative to control SD rats. The changes in glomerular permeability to albumin were correlated with the degree of proteinuria in these strains. These findings indicate that the fluorescence dilution technique can be used to measure Alb in populations of isolated glomeruli and provides a means to assess the development of glomerular injury in hypertensive and diabetic models.