This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with different organic wastes (sewage sludges, farm manure, and compost of municipal solid wastes) and the impact of an additional amount of Cu, Zn and Cd on N-mineralization. Net rates of mineralization fluctuated in the soil amended with organic wastes between 11.67 and 33.61 mg kg(-1). The decreasing order of mineralization, expressing a decreasing order of microbiological activity, was: soil+sludges > soil+manuer > soil+compost > soil. From the kinetic study, it was seen that the mineralization process could be divided into two main periods: the first was from soil moistening up to the fourth week and the second from soil 8 to week 16. The first phase of incubation was a period of microbial adaptation to the new environment of soil amended with organic wastes and enriched with Cu, Zn and Cd. This phase was often marked by N consumption-immobilization. The second phase Mas characterized by active kinetics of mineralization and intense microbial activity The influence of the organic amendments according to the value of N-o (the N-mineralization potential) was: N-o(soil) < N-o(compost) < N-o(manure) < N-o(sludges). The inhibitory effect of the added metals on N-mineralization was: Cd > Cu > Zn. For many reasons, the global effect of metals on N-mineralization was very variable. A sufficiently long latent time (8 weeks) wits needed for tolerant microorganisms to release or to start N-mineralization.