  An average value of the total-to-selective-extinction ratio R_V=3.8 +/- 0.4
in M31 is obtained by means of two independent methods and by use of the
analytical formula of Cardelli, Clayton & Mathis (1989). This result differs
from previous determinations as well from the `standard' value 3.1 for the
Milky Way. The derived individual extinctions for blue and red luminous stars
from the catalogue of Magnier et al. (1992) are in good agreement with recent
estimates for several OB associations in M31 and thus the issue about the
assumed optical opacity of the spiral disk still remains open. The presented
list of 113 red supergiant candidates in M31 with their extinctions and
luminosities contains 60 new objects of this type which are not identified in
other publications. It is supplemented with further 290 stars dereddened on the
base of results for their closest neighbors. The luminosity function of all red
supergiant candidates and the percentage of those with progenitors over 20
solar masses suggests that the evolution of massive stars in M31 resembles that
in other Local Group galaxies.
