  We report here our spectropolarimetric observations obtained using the
Espadons/CFHT high resolution spectrograph of two M dwarf stars which standard
models suggest are fully convective: EV Lac (M3.5) and HH And (M5.5). The
difference in their rotational velocity makes them good targets to study the
dependence of the magnetic field topology in M dwarfs on rotation. Our results
reveal some aspects of the field topology in EV Lac and HH And. We measured
mean longitudinal magnetic field strengths (Bz) in EV Lac ranging from 18+-3 G
to -40+-3 G. The Bz variations are seen to occur in a timescale of less than 50
minutes, significantly shorter than the rotation period, and are not due to a
flaring event. We discuss some formation scenarios of the Zeeman signatures
found in EV Lac. For HH And we could not detect circular polarization and thus
we place an upper limit to Bz of 5 G.
