Abstract: The present invention relates to the identification of new peptides and peptidomimetics which bind the CXCR4 receptor, capable of forming complexes with receptors for chemokines, in particular with CXCR4. The invention also relates to the use of these peptides for the treatment, prevention and diagnosis of diseases which involve chemokine receptors (i.e. neoplasias, metastases, HIV-1 virus infections), and also the mobilization of stem cells of hemopoietic precursors in the case of autologous transplants. Finally, the invention comprises pharmaceutical compositions and diagnostic kits comprising said peptides.