Highly deteriorated hardwoods require a great deal of attention in their conservation treatments. If these woods are allowed to air dry without stabilization, the size, shape, and surface detail will be completely distorted. Volumetric loss of dimension is generally more than 70 percent, the change due mainly to capillary tension collapse. However, cell wall shrinkage rates may also be different from those in normal wood. Both types of dimensional change may need to be controlled for stabilization to be successful. Highly deteriorated hardwoods are also very weak, subject to checking and failure both along and across the grain and subject also to denting. To prevent these problems, stabilization treatments should improve the strength and stiffness of the wood as well as control dimensional change. These woods have lost a large portion of their original cell wall material, and a selective removal of carbohydrate has occurred. Carbohydrate layers are greatly altered while lignin-rich layers remain intact. Treatment with peracetic acid removes lignin, revealing a layer of residual carbohydrate. Microscopic observation of this layer is valuable in determining the condition and uniformity of deterioration in waterlogged wood. With specific gravity and volumetric loss of dimension data, observations of the microscopic structure of waterlogged wood provide sufficient information to classify the wood as highly deteriorated or not highly deteriorated. These data also provide a quantitative means for evaluating the success of dimensional stabilization treatments.