  We report on WSRT observations of HI and OH absorption at z=0.885 towards the
radio lens PKS 1830-21, mm wave transitions of several molecular species have
already been observed at this redshift. At mm wavelengths the source structure
is dominated by two extremely compact components, the northeast (NE) and
southwest (SW) components. At lower frequencies the continuum emission is much
more extended and there is also a broad Einstein ring connecting the NE and SW
components. This means that the HI and OH spectra sample a much larger region
of the absorber than the mm wave spectra.
  The HI spectrum that we obtain is asymmetric, with a peak at -147 km/s with
respect to the main molecular line redshift of z=0.88582. Weak mm wave
molecular absorption has also been detected towards the NE component at this
same velocity. The HI absorption, however, covers a total velocity width of 300
km/sec, i.e. including velocities well to the red of molecular features
suggesting that it is spatially widespread. In OH we detect both the 1667 and
the 1665 MHz transitions. The OH spectrum has a velocity width comparable to
that of the HI spectrum, suggesting that it too is widespread in the absorber.
The lack of a prominent HI peak in the spectrum at the velocity corresponding
to the SW component, suggests that the galaxy responsible for the absorption at
z=0.885 has a central molecular disk many kpc in size, and that HI is deficient
in this central region. Our observations are sensitive to the large scale
kinematics of the absorber, and to first order the implied dynamical mass is
consistent with the lens models of Nair et. al. (1993).
