The adsorption of ammonium ion by three types of synthetic hydrated aluminum silicate (ZPC-10A, ZPC-50A and Molequlite 401) was studies to assess their possible utility as orally administered adsorbents for the treatment of uremia and ammoniemia. In vitro and preliminary in vivo studies suggest that ZPC-10A is promising as an adsorbent in terms of adsorption capacity, ion selectivity and resistance to acidity.