Preparation of novel poly(alkylamine)-derived hydrogels is described. Polymers are prepared via reaction of various diamines with dihalo compounds or diepoxides. N-substituted polymers are readily prepared by reaction of primary amines with dihalo compounds. The resulting covalently cross-linked polymers exhibit hydrogel behavior (high swell with water) when ionized to polyammonium species at low pH. At high pH, the polymers reside in the free base polyamine form and lose all hydrogel character (they no longer swell in water). Characterization of polymer structure with carbon-13 MMR, thermal analysis, and swell behavior reveals a structure which is highly branched and only loosely cross-linked. In the ionic polyammonium form thermal stability up to similar to 300 degrees C is observed. The polymers exhibit activity as bile acid sequestrants significantly superior to cholestyramine, as evidenced by their ability to efficiently bind quantities of cholate when tested in vitro. This behavior indicates that these hydrogels should be very useful for the treatment of hypercholesterolemia.