> Thank you again for this fast answer.
> The problem is that calling M-x R-mode under emacs usually works.
> But while calling R-mode with .emacs, it don't work anymore. And my R-scratch buffer is still in fundamental mode.
> If I find any answer, I will post it.
Perhaps M-x R-mode RET asks for parameters? Type C-h f R-mode RET and
see what's its usage.