Some physical and chemical properties of 1-to 2-mm aggregates obtained from casts and the burrowwall material of the earthworm species Lumbricus terrestris, Aporrectodea longa, and Aporrectodea caliginosa were determined in order to show the effects of earthworms on the stabilization of soil aggregates. The results were compared with those of the natural soil from the Ap horizon of a Parabraunerde (Luvisol, FAO). Both the tensile strength and the water stability of aggregates from casts and burrow-wall material were reduced compared with those of the natural aggregates but were increased compared with those of remoulded aggregates. These results indicate that to a great extent existing bonds are destroyed by earthworm ingestion. Nevertheless, earthworm activities are advantageous for the stabilization of reformed aggregates. The coarse sand fraction is reduced by selective ingestion by earthworms. The organic C content is increased by 4.1-21.0~ for burrow-wall material and by 21.2-43.0~ for casts. The carbonate content of aggregates from casts and burrow-wall material of L. terrestris was reduced by more than 50o7o, while that of A. longa showed no noticeable changes and that of A. caliginosa was increased by more than 60O/o. The total content of polysaccharides was increased by 35-87o7o for casts and by 33-46o/o for the burrow-wall material of all earthworm species. The most frequently detected monosaccharides were glucose, galactose, and glucosamine. L. terrestris appeared to have the strongest effect on the interparticle bonding of the reformed aggregates, measured both as tensile strength and water stability, followed by A. longa and A. caliginosa.