This International Standard describes a method for determining the inhibition of the growth and reproductive capability of higher plants by soils under controlled conditions. Two species are recommended: a rapid-cycling variant of turnip rape (Brassica rapa CrGC syn. Rbr) and oat (Avena sativa). The duration of test should be sufficient to include chronic endpoints that demonstrate the reproductive capability of the test plants. By using natural test soils, e.g. from contaminated sites or remediated soils, and by comparing the development of the test plants in these soils with reference or standard control soils, the test can be used to assess soil quality, especially the function of the soil as a habitat for plants. Annex A describes modifications allowing use of the chronic plant assay for the testing of chemicals incorporated into soil. By preparing a dilution series of a test substance in standard control soils, the same endpoints can be measured to assess the chronic toxicity of chemicals. This method is not applicable to volatile substances, i.e. substances for which H (Henry’s constant) or the air/water partition coefficient is greater than 1, or for which the vapour pressure exceeds 0,013 3 Pa at 25 °C.