Elemental abundances of noble gases in siliceous microfossils from deep-sea sediments were determined employing the stepwise heating technique. Almost all the Ar and about 80% of the total Kr were released in the lowest temperature fraction of 800 ¿C. Only Xe was released in higher temperature fractions, suggesting that Xe was tightly trapped inside silica. The Xe concentrations of siliceous microfossils seem to lie on the correlation line of Xe content vs. the temperature of geothermal orgin. The selective trapping of Xe at high temperatures in amorphous silica indicated the possibility that amorphous silica is the reservoir of the terrestrial ''missing'' Xe. However, quantitative calculation showed that the total amount of Xe in amorphous silica quantitative calculation showed that the total amount of Xe in amorphous silica ¿ American Geophysical Union 1989