  We present MERLIN observations of the continuum (both 1.6 and 5 GHz) and OH
maser emission towards Arp220. the correct spatial configuration of the various
componnents of the galaxy is revealed. In the eastern component the masers are
shown to be generally coincident with the larger scale continuum emission; in
the west, the masers and continuum do not generally arise from the same
location. A velocity gradient (0.32+/-0.03km/s/pc) is found in the eastern
nuclear region in MERLIN scales; this gradient is three times smaller than seen
in OH and implies that the OH gas lies inside the HI. A re-analysis of
previously presented global VLBI data (Lonsdale et al. 1998) reveals a very
high velocity gradient (18.67+/-0.12km/s/pc) in one component, possibly the
site of a heavily obscured AGN.
