Abstract: An electrolytic hygrometer is provided which comprises a hollow cylinder having first and second shoulders and a ceramic substrate containing an electrolytic cell circuit pattern mounted on the second shoulder of the hollow cylinder and extending upwardly inside the hollow cylinder toward the first shoulder. A permeable membrane is provided which is removably mounted on the first shoulder by means of a sandwiched configuration comprising a first mounting ring, a first porous stainless steel protective disk, the membrane, a second porous stainless steel protective disk, and a second mounting ring. A ring nut is employed to removably fasten the membrane's sandwiched configuration against the first shoulder of the hollow cylinder.