The acetone soluble lignins of Pinus radiata wood, which had been steam exploded by the Australian Siropulper process, both with and without SO2pretreatment, have been examined by13C NMR spectroscopy. The marked structural effects of SO2pretreatment are discussed. A brief comparison of the lignins from wood treated by the Siropulper and Canadian Iotech processes (without SO2pretreatment) is also presented.