Redesign of the Severinghaus pCO2 and the Clark pO2 electrodes yields electrodes which are easier to make and assemble. When used with a new membrane material, paraffin-treated Millipore filter paper, the redesigned Severinghaus pCO2 electrode gives 99% response in 15 sec for a 40 mm Hg change in pCO2 in the region of 15–60 mm Hg pCO2 in either gas or water phase. The redesigned Clark pO2 electrode when used with treated Millipore paper gives 99% of final response in 1.24 sec for a 155 mm Hg change of pO2 in the gas phase in the range 0–160 mm Hg pO2. In aqueous solutions this electrode gives 99% response in 30 sec. Severinghaus electrode; polarographic oxygen electrode; pCO2 measurement; pO2 measurement Submitted on March 19, 1963