The structures of the three title isomers, namely 4-(2-methylanilino) pyridine-3- sulfonamide,(I), 4-(3-methylanilino) pyridine-3-sulfonamide,(II), and 4-(4-methylanilino) pyridine-3-sulfonamide,(III), all C12H13N3O2S, differ in their hydrogen-bonding arrangements. In all three molecules, the conformation of the 4-aminopyridine-3- sulfonamide moiety is conserved by an intramolecular N—H⋯ O hydrogen bond and a C ...