It is shown that the MP2(fc)/6-311 + G**//HF/6-31G*+ZPE(HF/6-31G*) theoretical model reproduces very well the experimental proton affinities (PAs) of aminoalkanes and of some of their fluoro derivatives as well as the PAs of aniline and pyridine. In all molecules considered the nitrogen is most susceptible to proton attack. PA values of amino derivatives including aniline are shown to be linearly dependent on the nitrogen lone-pair s character. Increments I(X)(alpha) are derived for the amino group and the pyridine nitrogen, which extend the set of substituent increments derived previously for an additive estimation of PA values of polysubstituted benzenes.