Two experimental plots of an agricultural land contaminated with radioactive elements (uranium, radium thorium) and toxic heavy metals (copper, zinc, cadmium) were treated by two different biotechnological in situ methods. The soil in this land was characterized by a negative net neutralization potential, and the soil pH was in a slightly acidic pH range (from 4 to 5). The contaminants were located mainly in the upper soil layers (mainly in the horizon A). Both methods were connected with the initial solubilization of the contaminants. Water acidified with sulphuric acid was used as a leach solution. The solubilization was mainly a result of the activity of the indigenous soil microflora. This activity was enhanced by suitable changes in the levels of some essential environmental factors, such as water, oxygen and nutrient content of the soil. The first method was then connected with the removal of the dissolved contaminants from the soil through the soil effluents. The second method was based on the transfer of the contaminants into the deeply located soil horizon B-2, where they were immobilized mainly as a result of the activity of the indigenous sulphate-reducing bacteria. Their activity was enhanced by injecting water solutions of organic compounds into the horizon B-2 through boreholes located in the relevant experimental plot.