The effects of a white rot, brown rot and soft rot fungus on beech, birch and Scots pine sapwood have been studied. Use of the scanning electron microscope has permitted clearer observation of the patterns of wood cell-wall lysis than has previously been possible using other techniques. The observations made emphasise the importance of the structure and composition of the tertiary wall layer, and it is concluded that the SEM technique can be of value in the further investigation of certain enzyme characteristics and cell wall composition.