A re-usable sterilizer test device is disclosed which is comprised of at least two parts which are releasably connected together. An indicator device which changes colour in the presence of steam after a certain time period is deposited within the two parts. One or both of the bodies is manufactured from a material having a predetermined degree of porosity as regards steam and is generally cylindrical or spherical so that the outer surface of said one or both bodies forms a significant and substantial portion of the external surface of the assembled device. Steam penetrates the porous body and passes into a cavity inside the body from where the steam can move internally of the device through suitable passageways and into a chamber where the indicator is located.