In 22 patients non-compartmental analysis was applied to plasma disappearance curves obtained after a single injection of polyfructosan to measure volume of distribution (Vd), renal clearance (Cl) and the whole body permeability-surface area product (PdS) of the indicator. It was found that introduction of the theoretical plasma concentration at time zero, calculated as the injected amount divided by the plasma water volume independently determined, to the curves was necessary to determine the initial slope of the curve and subsequently calculate the PdS. This 'initial phase' approximation had negligible effect on the calculations of Vd and Cl. The approximation, however, allowed extension of the non-compartmental analysis to include calculation of the whole body PdS. The whole body PdS for polyfructosan was found to be 0.68 ml/100g X min or 429 ml/min. Assuming a capillary surface area of the whole human body of 50 cm2g-1, the average whole body diffusional permeability coefficient, Pd, for polyfructosan was found to be: 0.23 X 10(-5) cm X sec-1.