  We study the effects of the RKKY interaction between magnetic impurities on
the mesoscopic conductance fluctuations of a metal ring with dilute magnetic
impurities. At sufficiently low temperatures and strong magnetic fields, the
loss of electron coherence occurs mainly due to the scattering off rare pairs
of strongly coupled magnetic impurities. We establish a relation between the
dephasing rate and the distribution function of the exchange interaction within
such pairs. In the case of the RKKY exchange interaction, this rate exhibits
1/B^2 behavior in strong magnetic fields. We demonstrate that the Aharonov-Bohm
conductance oscillations may be used as a probe of the distribution function of
the exchange interaction between magnetic impurities in metals.
