  We demonstrate that it is crucial to account for the evolution of the
starburst population in order to derive reliable numbers of O stars from
integrated spectra for burst ages t > 2 - 3 Myr. In these cases the method of
Vacca & Conti (1992) and Vacca (1994) systematically underestimates the number
of O stars. Therefore the current WR/O number ratios in Wolf-Rayet (WR)
galaxies are overestimated. This questions recent claims about flat IMF slopes
(alpha ~ 1-2) in these objects. If the evolution of the burst is properly
treated we find that the observations are indeed compatible with a Salpeter
IMF, in agreement with earlier studies.
  Including recent predictions from non-LTE, line blanketed model atmospheres
which account for stellar winds, we synthesize the nebular and WR HeII 4686
emission in young starbursts. For metallicities 1/5 <= Z/Z_sun <= 1 we predict
a strong nebular HeII emission due to a significant fraction of WC stars in
early WR phases of the burst. For other metallicities broad WR emission will
always dominate the HeII emission. Our predictions of the nebular HeII
intensity agree well with the observations in WR galaxies and an important
fraction of the giant HII regions where nebular HeII is detected. We propose
further observational tests of our result.
