Salinity levels are rising in many freshwater environments, yet there are few direct measurements of salinity tolerance of organisms likely to be salt sensitive. The relative salinity tolerance to artificial seawater of macroinvertebrates from the Barwon River in Victoria, Australia, was assessed by measuring the 72-h lethal concentrations required to kill 50% of individuals (LC50). LC50 values ranged from an electrical conductivity of 5.5 to 76 mS cm-1 (mean 31 mS cm-1, n = 57) and followed a log-normal distribution. The most salt-sensitive groups tested were Baetidae (LC50 value range: 5.5-6.2 mS cm-1), Chironomidae (10 mS cm-1) and several soft-bodied non-arthropods (Oligochaeta, Gastropoda, Nematomorpha, Tricladida and Hirudinea; 9-14 mS cm-1). Other groups, from least to most tolerant, were non-baetid Ephmeroptera (>12.6-15 mS cm-1), Plecoptera (>12.6->20 mS cm-1), Trichoptera (9->26 mS cm-1), Corixidae (18-26 mS cm-1), non-corixid Hemiptera (33-44 mS cm-1), Coleoptera (19-54 mS cm-1), Hydracarina (39 mS cm-1) and Odonata (30-55 mS cm-1), and macrocrustaceans (Decapoda, Isopoda and Amphipoda; 38-76 mS cm-1).