In the present work, some of the factors that influence the rejection and fouling patterns observed during sugar-beet pulp extract ultrafiltration were examined. This material contained pectins, exhibiting a wide molecular weight distribution and a high tendency for aggregation. A dual pattern in the variation of the observed rejection coefficient with permeate flux was observed depending on the molecular weight: decreasing with increasing permeate flux for molecular weight fractions higher than 10 kD and the opposite for fractions less than 3 kD. Pectins were mainly responsible for the fouling properties of the pulp extract as ultrafiltration of purified beet-pectin solutions demonstrated. Efforts to alter the aggregation patterns in the extract both by changing the solutions' pH and by adding a reducing agent showed that the interaction between different components of the extract, rather than between pectins only, had a positive effect on the fouling behaviour.