  The Odin satellite, launched in Feb. 2001, is equipped with a 1.1-m
submillimetre telescope. Odin was used to observe the 557 GHz line of water
with high spectral resolution in 12 comets between 2001 and 2005. Line shapes
and spatial mapping provide information on the anisotropy of the outgassing and
constraints on water excitation, enabling accurate measurements of the water
production rate. Five comets were regularly observed over periods of more than
one month to monitor the variation of their water outgassing rate with
heliocentric distance. Observing campaigns have been generally coordinated with
ground-based observations of molecular lines at Nan\c{c}ay, CSO or IRAM 30-m
telescopes to obtain molecular abundances relative to water.
  Thanks to Odin's frequency coverage, it was also possible to detect the
H_2^18O 548GHz line, first in comet 153P/Ikeya-Zhang in April 2002 (Lecacheux
et al., 2003) and then in comets C/2002 T7 (LINEAR), C/2001 Q4 (NEAT) and
C/2004 Q2 (Machholz). The ^16O/^18O isotopic ratio (\approx450) is consistent
with the terrestrial value. Ammonia has been searched for in three comets
through its J_K = 1_0-0_0 line at 572 GHz and was tentatively detected in
C/2001 Q4 and C/2002 T7. The derived abundances of NH_3 relative to water are
0.5 % and 0.3 %, respectively, similar to values obtained in other comets with
different techniques.
