A simple high‐vacuum pump which combines large areas of evaporated barium with a source of ionization is described. Though of moderate pumping speed this barium‐ionization pump is capable of maintaining high vacuum in unoutgassed sealed‐off systems even in the presence of organic sealing materials. Simplicity is achieved by use of externally applied heat for barium evaporation which may be performed initially or periodically as required. Data are presented which show the capabilities and limitations of such absorption systems. The similarity of this absorption process to that producing oxidation of metals in air is noted.