Development of polysaccharide fouling layers during dead-end membrane ultrafiltration is an inherent problem in water treatment and similar separation processes. Despite its practical significance, ultrafiltration membrane fouling under constant permeate flux J has received inadequate attention. Therefore, constant-flux experiments, with typical alginate model-solutions covering the flux range of practical interest (i.e. 10-100 L/m(2) h), are employed to obtain new insights into fouling layer characteristics. The specific resistance alpha, as the most representative fouling-layer property, is used for data interpretation. The behavior of resistance alpha, with increasing permeate volume, confirms that these gel-type layers are strongly affected by flux J and generally compressible. Layer compressibility is evident beyond an initial phase of membrane coverage by alginates. The initial resistance alpha(i), corresponding to thin developing layers and relatively small pressure-drop across the layer/"cake" Delta P-C, is independent of approximately linearly increasing with J. For all data-sets, variation of resistance a with Delta P-C is well correlated by a generalized expression involving (in addition to alpha(i)) two parameters, n and P-a, considered to represent layer/cake compressibility index and reference pressure, respectively; these parameters also increase (and are fairly well correlated) with J. The usefulness of these data is demonstrated in elucidating issues such as "critical flux" for this filtration mode. (C) 2014 Elsevier B.V. All rights reserved.