Total mercury (Hg) concentrations and lipid composition data, including fatty acid profiles, for 61 midtrophic species (fish, cephalopods, crustaceans) collected from continental slope waters off south-east Australia were examined. Overall, Hg concentrations were greatest in fish (0.01-0.30 mu g g(-1) ww) (with highest content found in barracouta (Thyrsites atun) and whiptails (Coelorinchus fasciatus)), compared with cephalopods (0.01 and 0.17 mu g g(-1) ww) and crustaceans (<0.04 mu g g(-1) ww). Lipid composition varied between species and within habitat (mesopelagic, bathypelagic and benthic). Mean total lipid content ranged from 0.5 to 13.2% ww, and in most species was dominated by triacylglycerols and phospholipids. In fish and squid, fatty acids were generally dominated by monounsaturated fatty acids, whereas crustaceans were higher in polyunsaturated fatty acids. Multidimensional scaling analyses separated species into groupings according to their fatty acid composition that could be interpreted with taxonomic, trophic and habitat information. Discriminant function analyses indicated the most influential (predictor) fatty acids for each group. Biochemical profile classifications can be used in wider trophodynamic studies to understand contaminant transfer, trophic relationships and community dynamics in marine environments.