  A finite group R is a CI-group if, whenever S and T are subsets of R with the
Cayley graphs Cay(R,S) and Cay(R,T) isomorphic, there exists an automorphism x
of R with S^x=T.
  The classification of CI-groups is an open problem in the theory of Cayley
graphs and is closely related to the isomorphism problem for graphs. This paper
is a contribution towards this classification, as we show that every dihedral
group of order 6p, with p>3 prime, is a CI-group.
