  We show that any non abelian free group $\F$ is strongly
$\aleph_0$-homogeneous, i.e. that finite tuples of elements which satisfy the
same first-order properties are in the same orbit under $\Aut(\F)$. We give a
characterization of elements in finitely generated groups which have the same
first-order properties as a primitive element of the free group. We deduce as a
consequence that most hyperbolic surface groups are not $\aleph_0$-homogeneous.
