The present invention provides improved methods and compositions for therapeutically controlling and/or reducing serum phosphate levels in animals and mammalian patients. The methods comprise administering to the patient an amount of a dendrimer composition effective to prevent absorption of substantial amounts of phosphate from the patient's GI tract. In a preferred version, a dose of between 2.5 and 15 grams per day is effective to prevent over 80% of phosphate present in the patient's GI tract from being absorbed. The dendrimer composition may comprise a hydrochloride, hydrobromide, hydroacetate or hydroanionic form.