In this paper the effect of two pre-treatment methods are compared experimentally for the filtration of (i) a spent sulphite liquor (17.8 wt.% dry solids) using a 20 kg mol(-1) molar mass cut off (MMCO) fluoropolymer membrane and (ii) a molasses solution (45 Brix) using a polysulphone (Psi) membrane (1.5 mu m pore size). Both feeds are industrially relevant, and subject to severe fouling issues when membranes are used in their subsequent processing. The pre-treatment methods evaluated were: (i) conditioning with water at 60 degrees C only [Protocol 1], and (ii) conditioning with water at 60 degrees C followed by cleaning with 0.5 wt.% NaOH [Protocol 2]. Results are presented that confirm the benefits of sodium hydroxide preconditioning upon performance, supporting the suggestion by some membrane manufacturers that this step be included as part of the pre-treatment protocol. (C) 2011 Elsevier Ltd. All rights reserved.