Standard computer techniques were developed for computation of ΔG° values from potentiometric titration data and ΔH° values from calorimetric titration data. The procedures developed can be used for any systems having the general equations HA = W^+ + A^- ; H_2A = 2H^+ + A^2- ; and H_3A = 3H^+ + A^3-, where the proton ionizations may be consecutive or simultaneous. The thermodynamic values ΔG°(K), ΔH° and ΔS° were determined for the ionization of protons from the protonated compounds methionine (-NH_3^+ group only), phosphoethanalomine and phosphoserine. The compounds studied were selected because they contain one, two and three ionizable protons respectively.