Applicable to all types of styrene-butadiene rubber (SBR) including oil-extended types and also for block copolymers containing up to 50 % (m/m) of styrene. The procedure may give low results when the content of mineral fillers insoluble in nitric acid exceeds 5 % (m/m). The principle is based on the extraction of a test portion with acetone and digestion with nitric acid to oxidize the styrene to p-nitrobenzoic acid. Extraction of the p-nitrobenzoic acid with diethyl ether. Extraction of the p-nitrobenzoic acid from the ether with sodium hydroxide solution and spectrometrical measurement in the ultraviolet spectral region. Cancels and replaces ISO 5478:1980, of which it constitutes a technical revision.