  {Although there is considerable evidence supporting an ubiquitous magnetic
field in solar/stellar photospheres, its impact in the determination of
abundances has never been quantified. In this work we investigate whether the
magnetic field plays a measurable role for this kind of studies. To that end,
we carry out simulations of spectral line formation in the presence of a
magnetic field, and then use those profiles to derive the abundance of several
atomic species (Fe, Si, C and O) neglecting the magnetic field. In this way, we
find that the derived iron abundance can be significantly biased, with
systematic errors up to 0.1 dex. In the case of silicon, carbon and oxygen
their role is very marginal (errors smaller than 0.02 dex). We also find that
the effect of the magnetic field strongly depends on its inclination with
respect to the observer. We show that fields that are aligned with the observer
lead to an underestimation of the real abundance, whereas more inclined ones
overestimate it. In the case of a mixture of fields with different inclinations
these effects are likely to partly cancel each other out, making the role of
the magnetic field even less important. Finally, we derive a simple model that
can be used to determine the suitability of a spectral line when we wish to
avoid the bias introduced by the neglect of the magnetic field.
