This International Standard specifies a method, by analysis of inorganic carbon, for the evaluation in an aqueous medium of the ultimate aerobic biodegradability of organic substances at a given concentration of microorganisms. This International Standard is applicable to organic compounds which are: a) water-soluble under the test conditions; b) poorly water-soluble under the test conditions, in which case special measures may be necessary to achieve a good dispersion of the compound (see ISO 10634); c) volatile; d) not inhibitory to the test microorganisms at the concentration chosen for the test. In this test, biogenically produced inorganic carbon is measured in situ in the test vessels in such a manner that the rate measured nearly equals the rate of microbial production.