Removal of toxins or metabolites from the circulation by the passing of blood, within a suitable extracorporeal circuit, over semipermeable microcapsules containing adsorbents (e.g., activated charcoal) or enzymes, other enzyme preparations (e.g., gel-entrapped microsomes, membrane-free enzymes bound to artificial carriers), or other adsorbents (e.g., various resins, albumin-conjugated agarose).