AbstractAcidity constants at 20° and the ionic strength μ = 0,1 were determined for substituted benzenesulfonamides and two series of substituted benzenesulfonanilides. pK values are plotted versus Hammett's σ constants and ϱ values are calculated. ϱ = 1,06 is obtained for benzenesulfonamides, ϱ = 1,16 for benzenesulfonanilides substituted on the S side, and ϱ = 1,74 for benzenesulfonanilides substituted on the N side. In the latter series, σ values must be applied for p‐NO2and p‐CH3CO. ϱ values found in this work are compared with those for other reactions, and they are discussed in terms of electrostatic field effects, inductive and mesomeric effects. It is concluded that direct field effects and electronic effects transmitted through the atom chain equally contribute to the free energy change caused by a