The method specified applies to organic compounds which are soluble, non-volatile (or which have a neglible vapour pressure), not lost by foaming from the test solution, not significantly adsorbable on glass and activated sludge, not inhibitory to the test microorganisms. Its principle is comparison with the comparison of dissolved organic carbon in the effluent from a control unit. Annex A gives examples of results of the test on various compounds, Annex B typical control values.