The maturing process of cattle manure composting was characterized by elemental composition analysis, solid-state C-13 NMR spectra, respiratory quinone profiles, and a germination index using Brassica campestris L. Three separate experimental runs were conducted in which cattle manure compost was matured for up to 12-18 months after 14 days of thermophilic composting. The microbial biomass and diversity that developed during thermophilic composting were maintained at high levels for several months, and then decreased significantly. This change was accompanied by a decreased content of carbon, especially carbohydrate carbon, and a decrease in phytotoxicity. During this period, the alkyl C/O-alkyl C ratio increased, resulting in decreased C/N ratios, microbial biomass, and microbial diversity. The proportion of Actinobacteria increased slightly and this was associated with the disappearance of phytotoxicity. (c) 2005 Elsevier Ltd. All rights reserved.