Columns of aggregates of a soil, which slakes into microaggregates of about 30 � diameter as well as swelling on quick wetting, were examined by high speed photography during infiltration. Because of the collapse of the original structure of surface layers, the supply of water to deeper layers is restricted. Examination of motion pictures and magnified stills for the depth zone just below the collapsed surface layer provides a description of the phenomena occurring during the advance of the front. These phenomena are discussed in terms of limitations of the procedure used, the mechanism of wetting, the displacement of particles, infiltration behaviour, and the nature of swelling and slaking in these systems.