Soils from many portions of the Mediterranean region are subjected to progressive degradation as a result of erosion by wind and water. As a consequence, the fertility level of these degraded soils is declining. This report studied the dehydrogenase activity of 18 soils, all of which were subjected to processes of erosion, in order to ascertain whether such activity could serve as a marker of the microbial activity of a degraded soil. The dehydrogenase activity of the soils studied was not correlated with their organic matter content, indicating that total organic matter was not representative of the microbial activity of degraded soil. An analysis of principal components showed a similar behavior between other indices of microbial activity (basal respiration and biomass carbon) and the dehydrogenase activity values. This data confirmed that dehydrogenase activity can be used as a sensitive marker of soil degradation and soil microbial activity.