A chemical, chemical-physical and biochemical comparison was made between two municipal wastes of differing degrees of maturity (one fresh and the other composted) and a variety of organic materials (manure, leonardite and commercial HA). The chemical analysis revealed the different degrees of stability of the organic matter of the different materials. The enzymatic activities determined (urease, phosphatase, protease-BAA and beta-glucosidase) reflected the distinct nature of the organic materials studied, high values corresponding to little evolved organic matter and low values to stabilized organic matter Pyrolysis-gas chromatography was shown to be a suitable technique for characterizing organic materials, those most liable to mineralization being both municipal wastes and the manure. Although composting stabilizes the organic matter the structural-chemical composition of the compost was more similar to that of the fresh materials than to that of the more evolved materials. Copyright (C) 1996 Elsevier Science Ltd.