  We investigate how large lepton asymmetries affect the evolution of the early
universe at times before big bang nucleosynthesis and in particular how they
influence the relic density of WIMP dark matter. In comparison to the standard
calculation of the relic WIMP abundance we find a decrease, depending on the
lepton flavour asymmetry. We find an effect of up to 20 per cent for lepton
flavour asymmetries $l_f= {\cal O}(0.1)$.
