Carbon-14-labelled acetate was added to a heavy clay soil of pH 7.6 to study the transformation of acetate carbon into carbohydrate and amino acid metabolites during decomposition. The acetate was totally metabolized after 6 days of incubation at 25°C when 70% of the labelled carbon had been evolved as CO2. Maximum incorporation of trace-C into the various organic fractions was observed after 4 days when 19% of residual, labelled carbon in the soil was located in carbohydrates, 29 % in amino acids and 21 % in the insoluble residue of the soil. The curves showing the amounts of labelled carbon located in carbohydrates and amino acid metabolites show a curvilinear form during the first 30 days of incubation, indicating a variety of chemical compounds decaying at different rates. After this time, the decay curves became straight lines indicating a greater homogeneity of the metabolites. After 200 days of incubation, 2.2% of the labelled carbon originally added to the soil was located in carbohydrate metabolites, 7% in amino acid metabolites and 5% in the insoluble residue. The carbon in these fractions accounted for 77% of the total, residual, labelled carbon in the soil; 12% in carbohydrates, 40% in amino acids and 25% in the insoluble residue. The remainder was non-indentified, acid-soluble material. The carbohydrate metabolites originating from the labelled carbon decayed at a faster rate than the amino acid metabolites, indicating different protective mechanisms for these materials.