Sets out a method for the evaluation of the 'ready' biodegradability of organic compounds by aerobic microorganisms using a test medium. Measurement of the percentage consumption of oxygen within a closed flask at regular intervals allows evaluation of the biodegradability of the test compound. The method generally applies to compounds which are soluble in the test medium, do not reach or react with the CO(sub)2(/sub) absorbent, are volatile and not inhibitory to the test microorganisms at the concentration chosen for the test. Technically equivalent to ISO 9408:1991.