N In contrast to some hypotheses previously formulated, the features related to accessibility, flexibility and hydrophilicity are negatively correlated with the reactivity values of the dataset. Concerning accessibility and hydrophilicity, the hypothesis that the antigenic sites are on the surface, and thus probably hydrophilic, was recently confuted [9] . As a matter of fact, the analysis of the experimentally determined antigenic sites has revealed that the hydrophobic residues are more likely to be a part of antigenic sites if they occur on the surface of a protein.