Abstract. In laboratory experiments aggregates (1-2 mm) of a loamy colluvial soil and a silty luvisol soil were treated with the herbicides Gramoxone and Goltix WG, the active agent of Goltix WG Metamitron, lucerne meal and zinc. Lucerne meal clearly enhanced the aggre­gate stability of both soils. At dosages 10 and 50 times those of the recommended application rate also Goltix WG slightly enhanced the stability of aggregates 1-2 mm in both soils in the first experiment. There were no differences between Go!tix WG and its active agent Metamitron. The stabilization of aggregates can be attributed to an increased metabolism of easily degradable or­ganic substances. It was assumed that by this process stabilizing metabolic products were formed. The recalcitrant herbicide Gramoxone and zinc destabilized soil ag­gregates by reducing microbial activity at dosages 10 times the recommended application rate (Gramoxone) and 240 mg kg^-1 (Zn), respectively. Aggregate stability was more reduced in the colluvial soil showing lower aggre­gate stability than in the loamy colluvial soil.