  We compare two methods of distance determination to spiral galaxies using
optical/near-infrared (NIR) observations, the (I-K) versus M_K colour -
absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation
(TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the
usefulness of the NIR CM relation as a distance indicator for moderately to
highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and
90 deg); by avoiding contamination by dust the scatter in the CM relation is
significantly reduced, compared to similar galaxy samples published previously.
The CM relation can be used to determine distances to field spiral galaxies
with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with
previously published observations for which we can - to some degree - control
the effects of extinction, are consistent with a universal nature of the CM
relation for field spiral galaxies. High-resolution observations done with the
Hubble Space Telescope can provide a powerful tool to calibrate the relation
and extend the useful distance range by more than a factor of 2 compared to
ground-based observations. The intrinsic scatter in the NIR CM relation in the
absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy
of distance determinations on the order of 25%. Although we find an unusually
low scatter in the TFR (probably a statistical accident), a typical scatter in
the TFR would yield distances to our sample galaxies with uncertainties of only
about 15%. However, one of the main advantages of the use of the NIR CM
relation is that_we only need photometric data_ to obtain distance estimates;
use of the TFR requires additional kinematic data, although it can be used to
significantly greater distances.
