Previously reported values of pK(a) and K(HA(2)(-)) of sulfuric (first step) and nitric acids in acetonitrile derived from spectrophotometric indicator data have been revised. The revised values are 8.0(4), 2.7 x 10(3) mol(-1) dm(3) and 10.5(g), 1.2 x 10(3) mol(-1) dm(3), respectively. Both K-a and K(HA(2)(-)) of sulfuric acid are some 1.7 times smaller than those reported from potentiometric glass electrode data. An estimate of KaK(HA(2)(-)) of sulfuric acid was made from simultaneous spectrophotometric nitroaniline indicator and electrolytic conductivity measurements in solutions allowed to stand for various times. The glass electrode was used in mixtures of nitric acid and tetraethylammonium nitrate, pK(a) and K(HA(2)(-)) being 10.53 and 1.15 x 10(3) mol(-1) dm(3), respectively. The homoconjugation constant was verified from the increase in solubility of sodium nitrate in the presence of nitric acid. The protonation constant of aniline, 10(10.57) mol(-1) dm(3), was determined spectrophotometrically in aniline-anilinium perchlorate mixtures with p,p＇-dimethylaminoazobenzene and found to be in excellent agreement with the literature value.