I have cells and vertices in a circle defined with a local cylindrical system. I would like to rotate them with the same angle in this local system adding the desired angle to the theta coordinate. How can I do that ?

you have to use the vgen command

Since it is not very obvious for a beginner:

vgen, 2, 0, vset ,,, dx, dy,dz

is used to move or translate verticies in the currently active coordinate system.

Thanks a lot. Actually I found a good fonction befor your answers. The fonction vtrans allows to move the vertices from a local coordinate system to an other without keeping a copy of the old vertices, whereas vgen keeps a copy of the vertices. And I needed to define an other coordinate system with the desired angle. Job´s done !!