Abstract The durability of fibres in the lung environment after deposition could be a key factor in determining whether they accumulate to a sufficient tissue dose to cause pathological change. There is a shortage of information on the relative durabilities of respirable industrial fibres of various types. We describe a strategy for assessing the ability of different fibre types to persist in the lung milieu and to retain their biological activity. This is particularly important for the development of mesothelioma, where the long latent time that characterises this disease would be expected to exclude, from culpability, fibres that are not durable. We have combined a pre-treatment step in pH 5.0 or 7.0 with an assay that relies on the ability of fibres to damage the mesothelium. The long-term aim is to assess the impact that treatment in various pH solutions has on (a) fibre size/number, (b) loss of key elements, (c) the ability to damage the mesothelium. Such information should enable us to better predict the potential of fibres to cause mesothelioma.