This ingredient occurs as natural isoprene rubber (NR), synthetic isoprene rubber (IR), balata and gutta percha, in the total solids of NR or IR latices, in solid raw rubbers or in cured or uncured compounds. The method is applicable to these isoprene rubbers alone or in blends. Milling of the test portion as finely as possible is advisable. 2 tables and 2 figures. Annex for information on bibliography. - Replaces the first edition (ISO 5945:1982).