Four l‐glutamate neurotransmitter transporters, the three Na+‐dependent GLAST‐1, GLT‐1 and EAAC‐1, and the Cl−‐dependent EAAT‐4, form a new family of structurally related integral plasma membrane proteins with different distribution in the central nervous system. They may have pivotal functions in the regulation of synaptic L‐glutamate concentration during neurotransmission and are believed to prevent glutamate neurotoxicity. To investigate the specific physiological and pathophysiological role of the neuronal EAAC‐1, which is also expressed in kidney and small intestine, we have generated two independent mouse lines lacking EAAC‐1. eaac‐1−/− mice develop dicarboxylic aminoaciduria. No neurodegeneration has been observed during a period of> 12 months, but homozygous mutants display a significantly reduced spontaneous locomotor activity.