The number ratios Be / ( B + Be ) of Be to B–type stars in young , well studied clusters of the Galaxy , the LMC and SMC are examined .
In order to disentangle age and metallicity effects we choose clusters in the same age interval and for which reliable photometric and spectroscopic data are available .
Number counts are made for various magnitude intervals , and the results are found to be stable with respect to this choice .
In the magnitude interval M _ { \mathrm { V } } = -5 to -1.4 ( i.e .
O9 to B3 ) we obtained a ratio Be / ( B + Be ) = 0.11 , 0.19 , 0.23 , 0.39 for 21 clusters located in the interior of the Galaxy , the exterior of the Galaxy , the LMC and the SMC , respectively .

Various hypotheses for these differences are examined .
An interesting possibility is that the average rotation is faster at low metallicities as a result of star formation processes .
The much higher relative N–enrichment found by Venn et al .
( [ 1998 ] ) in A–type supergiants of the SMC , compared to galactic supergiants , also strongly supports the presence of more rotational mixing at low metallicities .
We discuss whether high rotational mixing may be the source of primary nitrogen in the early chemical evolution of galaxies .