The acidity constants (pK(a)) of oxime group containing nucleophiles like pralidoxime, butane 2,3-dione monoxime (BDMO), and some novel oxime-based functionalized nucleophiles, i.e., 3- and 4-hydroxyiminomethyl-1-alkylpyridinium bromides, have been determined spectrophotometrically at 27 degrees C in pure water and in a 50% (v/v) water-acetonitrile mixture, respectively. An effect of surfactant concentration on the pK(a) of pralidoxime has also been studied. It has been found that the pK(a) of pralidoxime was not affected by surfactant concentration.