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This study examines the effect of soil water content on aggregate stability and determines the relationships between the variation in soil stability and soil physical properties (texture, organic carbon, bulk density, pore size distribution and saturated hydraulic conductivity) in a microcatchment located in a semi-arid area of southeast Spain. The aggregate stability of soils was determined at three soil water contents (close to saturation, field capacity and air-dry) using a laboratory rainfall simulator technique. The aggregate stability for wetter conditions was higher than for the air-dry conditions for 85% of the samples tested. Furthermore, considerable difference in air-dry aggregate stability values was observed for predominant erosional and depositional zones within the microcatchment. This variability in air-dry aggregates stability was closely related to hydraulic properties and organic carbon content of the soil. Test on aggregate stability of air-dried soils are particularly appropriate for soils from semi-arid environments, and provide a more sensitive indicator of differences in the soil stability within the microcatchment than wetter samples. (C) 1998 Elsevier Science B.V. All rights reserved.