The inter-relationship between the point, planar defects and their complexes and low-stability pre-transitional states, phase transitions, structural transformations and stability of alloys with respect to structural-phase transformations in the low-stability state of systems is studied using BCC alloys as examples. It is shown that in the vicinity of structural-phase transformations in Copper-Palladium (Pd) alloys with a content of 40 at.% Pd the low-stability states are realized, which demonstrate a number of anomalous phenomena (e.g., anisotropy of atomic displacements, concentration inhomogeneities, stratification, heterophase fluctuations, nonlinearities in the dependencies of the lattice parameters and long-range order parameters, etc.) that prepare the system for transformation. Pre-transitional phenomena and low-stability states were commonly observed and investigated in detail in alloys undergoing MTs.