Current online methods of testing membrane integrity - turbidity and particle counting/monitoring are non-specific and offer moderate sensitivity. An alternative method of probing membrane integrity utilizing magnetically susceptible particles was evaluated as a means to improve both specificity and sensitivity. Compromised 0.6 mu m polycarbonate track-etched membranes were challenged with magnetically susceptible particles of 1 mu m diameter. Particles that breached the compromised membranes were successfully separated from the filtrate using a particle collector under the influence of a magnetic field. The particle capture efficiency decreased with higher filtrate flow velocity. The captured particles were readily released in the absence of a magnetic field allowing further concentration in a subsequent elution step and increased system sensitivity. Sample calculations show that the proposed technique is a plausible one for large-scale applications. (C) 2008 Elsevier B.V. All rights reserved.