Published online by Cambridge University Press: 14 August 2015
In many recent papers dealing with computations of evolutionary sequences for massive stars with mass loss, the evolutionary status of Wolf- Rayet stars has been discussed. When one whishes to compare these theoretical computations with observations, it is of great importance to know the masses of Wolf-Rayet stars, which unfortunately are well determined only in a few cases. Estimates of the masses are provided by binaries with WR type components. I will report here preliminary results of spectrographic observations for 4 WN+OB systems, with new information about the masses of their components.