pH values in the rhizosphere of peanut seedlings were measured with Sb micro electrodes in soils with a bulk pH between 3.9 and 7.7. Within 2–2.5 days the roots decreased soil pH to a minimum value which was linearly correlated with short term buffering capacity of the soils as determined by addition of HCl to soil suspensions. The greatest distance from the root surface where pH dropped significantly was found in soils with pH near 6. This maximum distance was also correlated with pH-buffering. The low buffering capacity for soils of pH near 6 seems to be valid for a large number of soils with different properties.