Enthalpies of ionization of glycine, dl-alpha- and dl-beta-alanines, nicotinic, picolinic, benzoic, and o-, m-, and p-aminobenzoic acids, aniline, pyridine, trigonelline, and ethyl nicotinate have been measured in 0-47.5 mol % ethanol in ethanol + water at 25-degrees-C. The results are coupled with previously reported thermodynamic dissociation constant values, and the values of the entropy changes have been calculated. The findings are discussed in terms of the solvent effect on the ionization of these compounds.