In this work, a dynamic membrane composed of Zr colloids was formed on a SS-316 porous tube to investigate its feasibility of concentrating hemoglobin (Hb) solutions. The very fine and uniform Zr colloids was prepared with the [SO4-2]/[ZrO+2] ratio below 0.5 and at 50 degrees C for 24 h. If the sulfate to zirconium ion ratio was above 0.5, the agglomeration would increase the Zr particle size to make it less desirable for separation applications. Depending upon the size of Zr colloids and the layer thickness, the dynamic membranes can offer a dextran MWCO from 300 kDa to 3 MDa. The rejection to Ho from those Zr dynamic membranes was at best 70%. However, if the Zr dynamic membrane was modified by a small amount of 2 MDa dextran, the resulting composite membrane exhibited 100% rejection to Hb molecules. Our results indicated that the adsorption of Hb on Zr colloids helped with its rejection by the dynamic membrane, but only at the expense of flux reduction. The presence of NaCl salt in Hb solution showed detrimental effects toward Hb rejection, which was probably caused by desorption of Hb from Zr colloids. However, at the isoelectric point of Hb (pH = 6.8), the detrimental effect due to NaCl was not observed. Brief comparison between this composite dynamic membrane and commercial polymeric membranes, YM-30 and PM-30 from Amicon, showed that our dynamic membrane had better rejection to Hb (100% versus 99.5% and 98.5%), but lower fluxes (7.7 versus 16.6 and 14.6 l/m(2) h).