The dissociation constants of substituted 2-(4-nitrobenzoylamino)alkanamides, N-[2-(4-nitrobenzoylamino)alkanoyl]pyrrolidines, and N-alkyl-4-nitrobenzamides have been measured spectrophotometrically in 60 and 80% v/v DMSO. The pKA values of these N-acids are discussed from the point of view of substituents at the acetamide α-carbon atom.