Cell wall material (CWM) was prepared from olive seed hull, which is heavily lignified and very tough. The material was cryomilled and delignified with chlorite/acetic acid for 9 h to give the holocellulose. Polymers were solubilised from the holocellulose by sequential extraction with cyclohexane-bans-1,2-diamine-NNN'N'-tetra-acetate (CDTA, Na salt), DMSO, 0.5, 1 and 4 M KOH and 4 M KOH + berate to leave the alpha-cellulose residue. The suspension of alpha-cellulose on neutralisation released a small amount of pectic material virtually free of xylan to give alpha'-cellulose. The polymers from the various extracts were fractionated by graded precipitation with ethanol prior to anion-exchange chromatography, and selected fractions were subjected to methylation analysis. During delignification, glucuronoxylans with relatively low degrees of polymerisation (DP) and xylan-pectic polysaccharide complexes linked to degraded lignin were solubilised. A proportion of the xylan-pectic polysaccharide complexes were solubilised by 0.5 M KOH. The major hemicellulosic polysaccharides of the olive seed hulls are glucuronoxylans, which occur as highly branched short chains, with DP of 30-60; or slightly branched chains with DP of 90-110. Partial acid hydrolysis of the major acidic xylan, gel-filtration chromatography and methylation analysis allowed us to propose a tentative structure for the major glucuronoxylan in which one residue of GlcpA occurs in each 14 continuously linked Xylp residues in a regular structure.