G-rich GT oligonucleotides with a different content of G clusters have been evaluated for their ability to exert cytotoxicity and to bind to nuclear-associated proteins in T-lymphoblast CCRF-CEM cells. Only the oligomers that did not form G-based structures or had a poor structure, under physiological conditions, were able to exert significant cellular growth inhibition effect. The cytotoxicity of these oligomers was related to their binding to the nuclear-associated eEF1A protein, but not to the recognition of nucleolin or other proteins. In particular, GT oligomers adopting a conformation compatible with G-quadruplex, did not exert cytotoxicity and did not bind to eEF1A. The overall results suggest that the ability of oligomers to adopt a G-quadruplex-type secondary structure in a physiological buffer containing 150 mM NaCl is not a prerequisite for antiproliferative effect in haematopoietic cancer cells. The cytotoxicity of G-rich GT oligomers was shown to be tightly related to their binding affinity for eEF1A protein.