  Heavy element abundances in extremely metal-poor stars provide strong
constraints on the processes of forming these elements in the first stars. We
attempt to determine precise abundances of strontium in a homogeneous sample of
extremely metal-poor stars. The abundances of strontium in 54 very or extremely
metal-poor stars, was redetermined by abandoning the local thermodynamic
equilibrium (LTE) hypothesis, and fitting non-LTE (NLTE) profiles to the
observed spectral lines. The corrected Sr abundances and previously obtained
NLTE Ba abundances are compared to the predictions of several hypothetical
formation processes for the lighter neutron-capture elements. Our NLTE
abundances confirm the previously determined huge scatter of the strontium
abundance in low metallicity stars. This scatter is also found (and is even
larger) at very low metallicities (i. e. early in the chemical evolution). The
Sr abundance in the extremely metal-poor (EMP) stars is compatible with the
main r-process involved in other processes (or by variations of the r-process),
as we briefly discuss.
