  Considering gravitino dark matter scenarios, we obtain the full
gauge-invariant result for the relic density of thermally produced gravitinos
to leading order in the Standard Model gauge couplings. For the temperatures
required by thermal leptogenesis, we find gaugino mass bounds which will be
probed at future colliders. We show that a conceivable determination of the
gravitino mass will allow for a unique test of the viability of thermal
leptogenesis in the laboratory.
