Comparing the observed and theoretical HR diagram for massive stars, it is concluded that at least 34 % of the stars within 2.5 kpc from the sun with initial ZAMS mass larger than 35 MO have not yet been detected. It is argued that the number of core helium burning pop I WR stars within 2.5 kpc from the sun may be as low as 26. If the progenitors of WR stars have initial ZAMS masses larger than 35 MO, one then concludes that the observed number ratio (core helium burning pop I WR stars) / (WR progenitors) within 2.5 kpc from the sun ranges between 0.05 and 0.09.