Metabolites such as ammonia and lactic acid formed during mammalian cell culture can frequently be toxic to the cells themselves beyond a threshold concentration of the metabolites. Cell culture conducted in the presence of such accumulated metabolites is therefore limited in productivity. This work demonstrates with laboratory data that a nonporous ion-exchange membrane of the perfluorinated sulfonic acid type can be used to contact the culture medium, and ammonia removed selectivity from the medium without disturbing the process. The technique of pervaporation showed particular promise in this regard. The pervaporation used with inert gas sweep on the permeate side was found superior to that used with vacuum application.