Increase of VPAC receptor s binding to the (16)gamma-glutamyl diaminopropane vasoactive intestinal peptide (VIP-DAP) agonist, a vasoactive intestinal polypeptide (VIP) structural analogue containing a positive charge at position 16, has confirmed the importance of a positive charge at this site. By investigating the effect of distance from the peptide backbone Calpha of a positive charge in position 16, data are reported here concerning: (i) a novel chemical method used for the synthesis of a new family of (16)gamma-glutamyl diamine VIP derivatives differing among them for single carbon atoms and including diaminoethane (VIP-DAE2), diaminopropane (VIP-DAP3), diaminobutane (VIP-DAB4), diaminopentane (VIP-DAP5), and diaminohexane (VIP-DAH6); (ii) functional characterization of these compounds on human VPAC1 and VPAC2 receptors. In more detail, the EC50 and IC50 values, when measured as a function of the alkylic chain length, show in more detail, that the use of VIP-DAB4 derivative changes the IC50 but not the EC50, thus indicating on hVPAC2 receptor an unexpected relationship between binding and activity that differs from that obtained on hVPAC1.