During tumbling of Salmonella, the helical shape of flagellar filament changes and this is called flagellar polymorphic transformation. We proposed amino acid residues involved in this polymorphic transformation as the key residues. Among mutants with a second mutation in them, flagellar filaments of A427T transformed from curly through coil to curly within a narrow pH range from 10.3 to 11.4. It is suggested that lysine residue is responsible for from curly to coil polymorphic transformation at pH 10.4 and that for from coil to curly at pH 11.3 maybe arginine residue related. Results from Q117A and R431K also will be discussed.