A high-performance liquid chromatography (HPLC)-method was established to quantify the development and degradation of DNA, rRNA and tRNA in the Langenalb soil filter fed with combined sewer overflow. The DNA served as a parameter for the microbial biomass and the RNA/DNA ratio for the growth rate. For nucleic acids, quantification samples were taken at different depths and sections of the clogged and the unclogged soil filter. Highest DNA concentrations were found at a depth of 0-2 cm in the clogged soil filter. During a starvation period of three months the DNA- and RNA-concentrations decreased twofold at depths between 0-8 cm. The higher nucleic acid concentrations at depths of 10-40 cm in the unclogged soil filter were attributed to a shift of the starved microorganisms. Similar RNA/DNA ratios in the clogged and the unclogged soil filter indicate similar growth rates and metabolic activities. It could be proven that the clogging of the soil filter was due to the microbial biomass and the DNA concentration, respectively.