Whole cell ‘phenotypic’ screening of chemical libraries has led to the identification of large numbers of compounds that inhibit the growth of asexual blood-stage Plasmodium falciparum parasites. The Medicines for Malaria Venture (MMV) has made available several chemically diverse sets of such compounds. We have adapted a series of biochemical/physiological assays to a 96-well plate format and used these to screen the MMV antimalarial compound collections. Some 7-9% of the antimalarials identified in phenotypic screens show the same characteristics: they cause an increase in parasite Na+ levels, an increase in the parasite’s cytosolic pH, and an increase in parasite volume; they inhibit the Na+ ATPase activity associated with the parasite membrane; and they have reduced efficacy against parasites with mutations in PfATP4, a putative plasma membrane Na+/H+ pump. The data are consistent with 7-9% of the antimalarials identified in phenotypic screens inhibiting PfATP4. The biochemical/physiological assays used here provide a ready means of identifying PfATP4 inhibitors.