Sugar-beet pulp was saponified and then hydrolysed with 0.1 M HCl at 80 degrees C for 72 h, and a rhamnogalacturonan fraction was isolated by ion-exchange chromatography on AG 1X8 resin. Four individual oligomers, and a mixture of oligomers with higher degrees of polymerization, were obtained by chromatography on BioGel P-4. They all presented the alpha-D-GalAp-(1[-->2)-alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1](n)-->2)-L- Rhap structure (with n greater than or equal to 2) The five fractions were submitted to hydrolysis with rhamnogalacturonase. The enzyme was active on oligomers with degrees of polymerization greater than or equal to 10, and gave as main products alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1-->2)-or-L-Rhap(1-->4)-D-GalAp and alpha-D-GalAp-(1-->2)-alpha-L-Rhap-(1-->4)-alpha-D-GalAp-(1-->2)-alpha-L -Rhap-(1-->4)-D-GalAp.