The metabolism of glutamine was studied in erythrocytes infected with Plasmodium falciparum, comparatively to normal cells, in presence or not of DON (6-diazo-5-oxo-L-norleucine) or acivicin, two glutamine antagonists which have been shown to inhibit the growth of P. falciparum in vitro. Extracellular glutamine was partially converted into glutamate using two routes corresponding to gamma-glutamyl transpeptidase (GGT) and glutaminase activities. In cells infected with mature trophozoites, the observed enhancement of the glutamine influx and of the glutamate formation was consistent with the enhancement of GGT and glutaminase activities.