Abstract: A gas diffuser assembly adapted for location in a volume of liquid or semiliquid material for dispersing minute bubbles of gas into the liquid. The assembly includes a housing formed of dense impermeable ceramic material and which defines an upwardly facing recess. A fitting formed of an inert material is located in the floor of the recess for connection to a gas supply tube. A diffuser element formed of porous ceramic material is secured to the housing over the recess to define an enclosed gas chamber. The diffuser disk and the housing are adhered together with a suitable cement.