The use of radiolabelled pesticides molecules'in research proved that some of the applied pesticides remain unexractable and become bound into the soil and other matrixes. Since the available methods to identify the nature of bound residues from parathion application were little effective, this study investigated the persistence and biorelease of C- parathion bound residues from soil to immediately, and 3 months after the pesticide application. Results proved that not only the pesticide, but also the soil characteristics and the aging of parathion into the soils determined the amounts and biorelease of bound parathion residues. These residues were weaker bound immediately after the parathion treatment than after an aging period. The rhizosphere did note have more influence on the biorelease than the microflora only, and most of the bound residues remained as still bound and inactivated into the soil.1995