For total air pressure and oxygen partial pressure measurements a hydrophobic membrane probe is used. The probe consists of a small membrane-covered chamber and two teflon capillaries. The probe represents an artificial, permanently air-filled pore which connects the soil atmosphere at a certain depth with a pressure transducer or an oxygen electrode placed on the soil surface. The soil water is excluded from the artificial gas phase by a water-repellent membrane highly permeable to air. The hydrophobic membrane makes the gaseous phase between soil and sensor continuous. This instrument was used in the field to follow changes in total air pressure and oxygen partial pressure in the soil atmosphere during water infiltration and drainage processes. The total pressure in the soil atmosphere and the partial pressure of its components strongly depend upon the continuity of the gaseous phase. This effect is shown in an undisturbed soil profile after a heavy artificial rainfall of 75 mm was applied within 2 hr.