  In this study we present simultaneous low-resolution longitudinal magnetic
field measurements and high-resolution spectroscopic observations of the cool
single giant FK Com. The variation of the magnetic field over the rotational
period of 2.4 days is compared with the starspot location obtained using
Doppler imaging techniques, V-band photometry and V-I colours. The
chromospheric activity is studied simultaneously with the photospheric activity
using high resolution observations of the Halpha, Hbeta and Hgamma line
profiles. Both the maximum (272 +/- 24 G) and minimum (60 +/- 17 G) in the mean
longitudinal magnetic field, <Bz>, are detected close to the phases where cool
spots appear on the stellar surface. A possible explanation for such a
behaviour is that the active regions at the two longitudes separated by 0.2 in
phase have opposite polarities.
