Abstract: The present application discloses a method for pre-treating a sample of a DNA/RNA adsorbing matrix (e.g. soil) suitable for extracting cell-derived (deoxy) ribonucleic acid therefrom, comprising the steps of: isolating a sample of a DNA/RNA adsorbing matrix, said sample comprising DNA/RNA-containing cells; and bringing the sample into contact with DNA of natural origin in a fragmented form (e.g. salmon sperm DNA) so as to essentially block said DNA/RNA adsorbing binding sites of said adsorbing matrix, said fragmented DNA being “unrelated” to the target DNA/RNA of said DNA/RNA-containing cells. The fragmented DNA of natural origin can be depurinated and/or freeze-dried. The application further discloses a method for extracting DNA/RNA from a sample and a kit useful for pre-treating samples.