When malaria parasites enter red blood cells they precipitate on influx of substrates necessary for their development. For example, intraerythrocytic trophozoites of Plasmodium falciparum use exogenous t-glutamine in increasing amounts during maturation from the ring-stage. This is made possible by a marked and selective increase in the permeability of the host cell membrane. Several compounds have now been identified as inhibitors of the l-glutamine influx induced by P. falciparum; they are all natural products - either analogues of l-glutamine, or related to indigenous traditional remedies for malaria. In this article, Barry El ford shows that although these compounds may not be of immediate practical value as antimolarials, they can provide valuable insight into the mechanisms underlying the regulation of these parasite-mediated transport processes.