In vertebrates, there are two variants of eukaryotic peptide elongation factor 1A (eEF1A; formerly eEF-1α), eEF1A1 and eEF1A2, which have three well-conserved domains (D(I), D(II), and D(III)). In neurons, eEF1A1 is the embryonic type, which is expressed during embryonic development as well as the first two postnatal weeks. In the present study, EGFP-tagged eEF1A1 truncates were expressed in cortical neurons isolated from rat embryo (E18-19). Live cell images of transfected neurons showed that D(III)-containing EGFP-fusion proteins (EGFP-D(III), -D(II)-III, -D(I)-III) formed clusters that were confined within somatodendritic domains, while D(III)-missing ones (EGFP-D(I), -D(II), -D(I)-II) and control EGFP were homogeneously D(I)spersed throughout the neuron incluD(I)ng axons. In dendrites, EGFP-D(III) was targeted to the heads of spine- and filopoD(I)a-like protrusions, where it was colocalized with SynGAPα, a postsynaptic marker. Our data inD(I)cate that D(III) of eEF1A1 meD(I)ates formation of clusters and localization to spines.