Abstract.-Straightforward and inexpensive analysis of blood constituents can provide quantifiable information on sub-lethal stress in an animal and a measure of their overall physical fitness. Such methods have been widely used on a range of marine and terrestrial species, primarily those of commercial or recreational importance. Freshwater crayfish in many regions of the world face a common suite of threats and threatening processes that include: exotic species (including other freshwater crayfish, associated diseases and parasites), habitat fragmentation and destruction, anthropogenic pollution, overexploitation and increased environmental temperature. Although some studies have investigated the effects of these on freshwater crayfish in-part (i.e., measured by gross symptoms), the subtle, often asymptomatic physiological effects are poorly understood. The analysis of haemolymph provides a simple, inexpensive, high resolution, portable (i.e., suitable for field analysis and assessment in remote areas) and non-lethal method for the evaluation of sub-lethal stress and immunocompetence status in freshwater crayfish. There is considerable scope for application of these existing techniques in conservation initiatives for rare and endangered freshwater crayfish in Australasia, in particular by providing: i) non-lethal stress assessments, ii) quantification of compromised health and iii) increased understanding of the physiological impacts from key threats and threatening processes.