On the basis of results of studies on experimental substantiation of MAC for miral in soil it has been found out, that the sub-threshold miral amounts according to the water-migrational, air-migrational, translocational and general sanitary indices of harmfulness equal 0.03, 3, 0.03 and 0.15 mg/kg respectively. Therefore, water-migrational and translocational indices are the limiting indices of harmfulness for miral. 0.03 mg per 1 kg of absolutely dry soil is recommended for miral MAC according to the acting substance.