This paper presents a model of the combined ultrafiltration-diafiltration process used by plasma fractionation centers to prepare human albumin by Cohn’s ethanol precipitation technique. This process consists of a predilution to lower the ethanol concentration C-a from 40 to 20%, a preconcentration phase to raise albumin concentration to similar to 80 g/l, a diafiltration to reduce ethanol concentration to 0.1 g/l and a final concentration of albumin to 210 g/l. Laboratory scale experiments were run with water-ethanol solutions of bovine albumin at various concentrations to determine, for each membrane rested, a correlation for the permeate flux as a function of C-a and C-p. The model was used to determine the effects of initial dilution and albumin concentration at diafiltration on a normalized process time, which is defined as the time necessary to process 1 kg of albumin with 1 m(2) of membrane. Optimal initial ethanol concentrations were found to depend upon the membrane material (30% for polysulfone, 16% for cellulose acetate) and the minimum process time was generally obtained when diafiltration was carried out at the maximum albumin concentration.