  X-ray and Sunyaev-Zel'dovich data of clusters of galaxies enable to construct
a test of the distance duality relation between the angular and luminosity
distances. We argue that such a test on large cluster samples may be of
importance while trying to distinguish between various models of dark energy.
The analysis of a data set of 18 clusters shows no significant violation of
this relation. The origin and amplitude of systematic effects and the
possibility to increase the precision of this method are discussed.
