  Helium abundances and atmospheric parameters have been determined from high
resolution spectra for a new sample of 46 bright hot subdwarf B (sdB) stars.
The helium abundances have been measured with high accuracy. We confirm the
correlation of helium abundance with temperature and the existence of two
distinct sequences in helium abundance found previously. We focused on isotopic
shifts of helium lines and found helium-3 to be strongly enriched in 8 of our
programme stars. Most of these stars cluster in a small temperature range
between 27000 K and 31000 K very similar to the known helium-3-rich main
sequence B stars, which cluster at somewhat lower temperatures. This phenomenon
is most probably related to diffusion processes in the atmosphere, but poses a
challenge to diffusion models.
