In this paper we address the long standing problem regarding the site for gas-phase protonation in aniline and substituted anilines. Our study reveals that DFT-based reactivity descriptors can reproduce the experimentally observed preferable protonation sites. However, it is found that the quantity s(k)(-)/s(k)(+), termed "relative nucleophilicity" and a measure of "local polarizability", produces more reliable results than the local softness, s(k)(-). The problem which sometimes arises in taking s(k)(-)/s(k)(+) as the reactivity. descriptor is also discussed.