Let a given particle symmetry be described by a reductive Lie group G. It is proved that the corresponding Weyl group W(R) acts canonically in all zero-weight spaces of G and hence, in particular, on observables. Moreover, it is shown how this W(R) action provides many physical relations, including those believed to be implied by G-transformation properties of observables. The results simplify a testing of symmetries based on various Lie groups (algebras). Their use extends beyond particle physics, e.g., to nuclear physics.