The patterns of incorporation of radioactivity from d-[U- 1 4 C]glucose into pectins, hemicelluloses and cellulose synthesised in differentiating cells of pine root-tips were analysed after sequential solvent extractions. The percentage composition of the radioactive glycosyl residues of hot-H 2 O- and Na 2 EDTA-+NH 4 -oxalate-+NaBH 4 -extractable cell-wall polymers was very similar. All sections of pine roots investigated synthesise a remarkably large amount of polymers rich in galactosyl and arabinosyl residues. These polymers may create in the wall a highly hydrated gel compartment structurally and physiologically important for the roots. The KOH-extractable polymers are rich in glucosyl and xylosyl residues.