The validity of the maximum hardness and minimum polarizability principles has been tested for HNO and CINO isomerization reactions. The former can be considered as a prototype of a two-state reaction and the latter as an example of reaction involving a system with a strong ionic character. For HNO both the (1)A' and (3)A " states have been considered. The hardness values along the reaction paths have been calculated by employing several working definitions and functionals in the framework of density functional theory. The correspondence between the profiles of hardness, polarizability, and energy has been investigated as a function of the reaction coordinate or the bond angle variation. The constancy of chemical potential has also been taken into account. No obvious relation between hardness or polarizability and energy profiles and between hardness and polarizability profiles has been observed.