We present details of 53 H20 masers located in the galactic plane between longitudes 260· and 326·. Twenty-one of these are new ones found at the sites of recently discovered OH masers. The properties of the individual masers are discussed, in particular the variability of sources known for several years and the high velocity emission exhibited by some masers. The association of H20 and OH masers has been investigated and out of 36 OH masers in this region of sky, a remarkably high number (34) have nearby H20 masers.

Twenty-five new H2 0 masers in the southern galactic plane have been discovered using a 22 GHz maser receiver on the Parkes telescope. The search was conducted at the locations of all the known 1665 MHz OH masers in the longitude range 340° through the galactic centre to 2°; of the 46 type I OH masers 38 are now found to have an H20 maser nearby; three other main-line OH emitters, possibly unusual late-type stars, also show H2 0 emission. We give an up-to-date tabulation of all 46 currently known H2 0 masers in the region which includes for completeness several H 2 0 masers with no readily detectable associated type I OH emission.Although a few very active regions of star formation harbour several masers, most commonly there is one, and usually only one, site of H2 0 maser emission near each OH maser. In a few wellinvestigated instances an H 2 0 maser is found to be slightly displaced spatially from its OH maser counterpart; this fact leads us to propose a 'binary' origin for such displaced pairs (perhaps applicable to most other H 2 0/OH pairs) in which the OH maser/compact HII region/new star is one of the pair, and a dense molecular cloud of stellar mass, not necessarily undergoing transformation to a star, is the other component giving rise to the H 2 0 emission.

A search in the direction of OH masers emitting at 1665 or 1667 MHz has yielded 11 new H 2 0 masers. The new sources are discussed individually. The overall statistics of the search show that out of a total of 55 OH masers in the 3° to 60° galactic longitude range at least 36 have H 2 0 maser counterparts.

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