The pK(a) of several alpha-phenylcarboxilic anti-inflammatory drugs in both isopropyl and tert-butyl alcohols have been determined by means of potentiometry. The dissociation constant values of their tetrabutyl-ammonium salts, which are necessary for computation of the acidity constants, have been determined conductometrically. The results show that both the drug acid strength resolution and the pH break in titration curves are greater in tert-butyl than in isopropyl alcohol, but both alcohols can be used in everyday titrations. Titrations in one commercial pharmaceutical preparation have been carried out successfully.