A new, microporous, uniformly reticulated preparation of cholestyramine is described. The preparation, cholpor, has a higher exchange capacity for chloride than does cholestyramine and swells very little in water. It is 15--20% more potent than chloestyramine in the in vitro binding of sodium cholate; moreover, the binding velocity is considerably higher than that of cholestyramine. Colestipol hydrochloride, also used as a reference anion-exchange resin, is about half as potent as the other two resins; its binding velocity is similar to that of cholpor. Cholpor may be prepared in a suspension form of good palatability. Preliminary clinical findings in short-term trials showed a cholesterol-lowering effect similar to that of cholestyramine with lower doses and fewer side effects.