The development and properties of a novel adsorbent system consisting of polyacrolein microspheres encapsulated in agarose is described. In the model system, the microspheres contain covalently bound bovine serum albumin. In practice any protein or ligands with primary amino groups may be covalently bound. Circulating antibovine serum albumin antibodies were adsorbed from whole blood or serum of rabbits or goats onto the microspheres. The capacity of this batch is 10 mg antibody adsorbed/gm wet weight beads. When the column is operated at less than capacity, 50%, 70%, 90% and 95% of the anti BSA is adsorbed in 30, 60, 120 and 180 min, respectively. Thus, relatively short periods of hemoperfusion may be used. The beads are biocompatible. There are negligible decreases of RBC; up to a 10% decrease of WBC and up to a 20% decrease of platelets in 3 hrs. The beads are stable; neither breakdown nor leakage was observed over a period of 3 months. High flow rates were readily obtained. The mean diameter of the microspheres is 0.2 mu; the mean diameter of the agarose polyacrolein microspheres beads (APAMB) is 1.0 mm. We can produce monodisperse beads of any given diameter ranging from 200 mu to 1 cm.