Sets out a method for the evaluation of the 'inherent' biodegradability of organic compounds. The procedure involves the measurement of the dissolved organic carbon content of effluent from a semi-continuous activated sludge unit dosed with a known concentration of the test compound. Comparison of these results with the results obtained with effluent from a control unit allows evaluation of the 'inherent' biodegradability of the test compound. The method generally applies to compounds which are soluble in the test medium, non-volatile, not lost by foaming of the test medium and not inhibitory to the test microorganisms at the concentration chosen for the test. Technically equivalent to ISO 9887:1992.