The basicity of the neutral form of some "standard" alpha-amino acids in gaseous and liquid phases is studied from the thermodynamic and statistical points of view. By using the proton transfer process (related to the amino group) in the gaseous and liquid phases, it is possible to carry out a thermodynamic cycle which allows the solvent effects to be separated from those intrinsic to neutral and protonated molecules. The basicity of these compounds seems to be mostly influenced by solute-solvent interactions (solvent effects). A monoparametric linear regression analysis leads (in terms of probability) to the hypothesis that it is uncertain if the side chains influence in the same way the basicity of the cc-amino acids in liquid and in gaseous phases.