  An extremely weak circularly-polarized signature was recently discovered in
spectral lines of the chemically peculiar Am star Sirius A (Petit et al. 2011).
This signal was interpreted as a Zeeman signature related to a sub-gauss
longitudinal magnetic field, constituting the first detection of a surface
magnetic field in an Am star. We present here ultra-deep spectropolarimetric
observations of two other bright Am stars, $\beta$ UMa and $\theta$ Leo,
observed with the NARVAL spectropolarimeter. The line profiles of the two stars
display circularly-polarized signatures similar in shape to the observations
gathered for Sirius A. These new detections suggest that very weak magnetic
fields may be present in the photospheres of a significant fraction of
intermediate-mass stars, although the strongly asymmetric Zeeman signatures
measured so far in Am stars (featuring a prominent positive lobe and no
detected negative lobe) are not expected in the standard theory of the Zeeman
effect.
