Thanks a lot Greglocock, I tried it before but "reflect" doesn't seem to be used to perform symmetry on a mesh.
Even in hypermesh-help, it's mentioned that "reflect= Moves the selected entities about the plane of reflection."
May be my question wasn’t clear enough, I had some symmetrical components (they have symmetrical plane) which require to be meshed, rather than meshing the whole component, I want only to mesh the half and perform a symmetry on it. At the end, I will obtain the whole component meshed (not only move elements from a side to the other like “reflect” does).
Have a good day.