The astrocytic L -glutamate ( L -Glu) transporter EAAT1 participates in the removal of L -Glu from the synaptic cleft and maintenance of non-toxic concentrations in the extracellular fluid. We have shown that niflumic acid (NFA), a non-steroidal anti-inflammatory drug (NSAIDs), alters L -Glu-induced EAAT1 currents in a voltage-dependent manner using the two-electrode voltage clamp technique in Xenopus oocytes expressing EAAT1. In this study, we characterised the effects of NFA on each type of ion-flux through EAAT1. NFA modulated currents induced by both L -Glu and L -aspartate ( L -Asp) in a voltage-dependent manner. Ion-substitution experiments revealed that the activation of additional H⁺ conductance was involved in the modulation of currents induced by L -Asp and L -Glu, but Cl⁻ was involved only with the L -Asp currents. NFA activated additional currents of EAAT1 in a substrate-dependent manner.