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An incubation experiment was performed to determine how the mixing of soil with municipal organic refuse compost affects C mineralization, growth of the microbial biomass, and changes in organic components, especially in the fractions of amino acids and amino sugars. Compost and soil differed in almost every parameter measured, with the organic C content of the compost representing only 10.8% of the dry weight. The fractions of K2SO4-extractable organic C and of non-hydrolyzable C were larger in the compost (1.24 and 62.9% of organic C, respectively) than in the soil (0.56 and 41.6% of organic C). These two fractions increased in proportion to the addition of compost, in contrast to amino sugar and amino acid C which were identified overproportionately in the mixture treatments, especially in the 30% compost treatment. Overproportionate increases in the microbial biomass C content and CO2 evolution rate were also measured in this treatment. The adsorption of compost colloids on the surface of regular soil silicates increased both the availability for microbial enzymes and the detectability for chemical analysis.