The Wolf-Rayet hydrogen puzzle -- an observational point of view
  Significant amounts of hydrogen were found in very hot early-type single WN stars in the SMC and the LMC. Recently, we found similar evidence in the Wolf-Rayet star of a short-period LMC binary. We discuss here the relevance of hydrogen for WR star classification, models, the relation to metallicity, and the GRB progenitors. 
C. Foellmi (ESO, Chile), S.V. Marchenko (U. Western Kentucky, USA),   A.F.J. Moffat (U. de Montreal, Canada)