The applicability of Laser-Induced Breakdown-Detection (LIBD) as an online membrane integrity monitoring system during ultrafiltration processes has been evaluated by linking a laboratory-scale membrane filtration test system to acoustic LIBD instrumentation. The results demonstrate that LIBD is a sensitive and reliable indirect online system suitable for testing and monitoring membrane integrity in ultrafiltration processes. Particles present in the filtrate can be detected continuously online using a fixed laser pulse energy (continuous mode). The LIBD monitoring system proved to be sensitive to nanoscale particles leaching through breaches in a membrane. In continuous mode 20 nm particles could be detected at concentrations as low as a few ng/L. This is superior in terms of both minimum detectable particle size and minimum concentrations to the turbidity measurement and particle counting methods that are commonly used for continuous online monitoring. Depending on the feed water characteristics and the membrane used, the LIBD system can be adjusted to specific processes by varying the measurement settings. Particle size distributions in the feed and filtrate can also be determined through non-continuous online LIBD measurements by varying the laser pulse energies (non-continuous mode), thus allowing the particle retention characteristics of the membrane to be analyzed. (C) 2014 Elsevier B.V. All rights reserved.