  For the purpose of deriving the helium abundances in chemically peculiar
stars, the importance of assuming a correct helium abundance has been
investigated for determining the effective temperature and gravity of main
sequence B-type stars, making full use of the present capability of reproducing
their helium lines.
  Even if the flux distribution of main sequence B-type stars appears to depend
only on the effective temperature for any helium abundance, the effective
temperature, gravity and helium abundance have to be determined simultaneously
by matching the Balmer line profiles. New MULTI NLTE calculations, performed
adopting ATLAS9 model atmospheres and updated helium atomic parameters,
reproduce most of the observed equivalent widths of neutral helium lines for
main sequence B-type stars and they make us confident of the possibility to
correctly derive the helium abundance in chemically peculiar stars.
  An application of previous methods to the helium rich star HD 37017 shows
that helium could be stratified in the magnetic pole regions, as expected in
the framework of the diffusion theory in the presence of mass loss.
