  Evolutionary models for massive stars, accounting for rotational mixing
effects, do not predict any core-processed material at the surface of B dwarfs
with low rotational velocities. Contrary to theoretical expectations, we
present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early
B-type dwarfs and (sub)giants that reveals the existence of a population of
nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects.
The low-rotation rate of several of these stars is firmly established, either
from the occurrence of phase-locked UV wind line-profile variations, which can
be ascribed to rotational modulation, or from theoretical modelling in the
pulsating variables. The observational data presently available suggest a
higher incidence of chemical peculiarities in stars with a (weak) detected
magnetic field. This opens the possibility that magnetic phenomena are
important in altering the photospheric abundances of early B dwarfs, even for
surface field strengths at the one hundred Gauss level. However, further
spectropolarimetric observations are needed to assess the validity of this
hypothesis.
