A method is described for the encapsulation of ion-exchange and adsorbent resins of native particle diameter 0.2-1.0 mm into agarose spheres of diameter 5-10 mm. Plasma components diffuse rapidly through the agarose coating, but blood corpuscles have no direct access to the resins. At least 0.3 g of resin can be incorporated into 1 g of the agarose beads, so that the effective surface area with regard to erythrocytes, thrombocytes, and leucocytes is reduced by a factor of at least 5, and up to 20, depending on the native resin particle size. Pulverised active charcoal, or resins in powder form can also be encapsulated in this manner. The haemocompatibility of the agarose coating seems to be considerably more acceptable than that of the adsorbents in their native state.