Human activity is one of the main causes of the physical, chemical and biological degradation of soils. This degradation implies a change in soil quality as it involves both a decrease in productivity and changes in the ecological functions of the soil. The objective of the present study was to investigate the effect of soil use on soil biochemical properties, with the aim of providing data that allow assessment of the usefulness of enzymatic activities as indicators of soil quality. In addition to physical and chemical properties, different hydrolase enzymes involved in the C, N, P and S cycles, and other biochemical properties, such as the microbial biomass C and soil basal respiration, were analysed. The results obtained allowed different conclusions to be reached regarding the main processes involving the biochemical properties in soils affected by human activity. The present study is a summary of a wider paper to be Publisher in Soil Biology and Biochemistry. This was presented as a Keynote to the 3 International Conference on Soil Enzymes (Viterbo, Italy), 15-19 July 2007 and, partly, as a invited Conference to the Segundo Simposio Internacional: Suelo, Ecologí a y Medioambiente (Temuco, Chile), 8-9 noviembre 2007.