Bt proteins are normally incorporated into soil together with plant residues, with sloughing of root cells, and potentially through the release of exudates from roots. Thus, Bt-toxins represent a possible risk for the soil ecosystem, and their potential impact on soil organisms may depend on their persistence. Under these circumstances, to understand the impact and risk of Bt-toxins on soil organisms, it is important to know how the different Bt-toxins vary in their degradation patterns. The differences in dissipation/persistence of Bt proteins in soil can be a function of soil type, environmental conditions, protein source (purified versus plant-produced), and the particular Cry protein examined. In this paper, we summarize insecicidal proteins synthesized by Bt plants commercially grown and the results of research regarding the persistance of Bt proteins in soil carried out in Romania and in other countries. These results provide evidence that Bt proteins do not accumulate in soil and reveal that the dissipation in soil of Bt proteins produced by genetically modified stacked maize was related to the type of endotoxin produced and not to the number of transgenes expressed.