Sediments from Mai Po Ramsar site, Hong Kong were in general shown to be highly toxic based on the results of four toxicity tests (Microtox solid-phase test, Daphnia mortality test, algal [Microcystis aeruginosa] growth inhibition test and ryegrass [Lolium perenne] seed germination/root elongation test). Sediment of the mudflat (which is open to Deep Bay, i.e., the pollution source) was the most toxic while sediment of gei wai 24g (an enclosed freshwater pond) was the least toxic. Results of biomarker studies (tilapia hepatic metallothionein; glutathione (GSH) and EROD activity using H4IIE rat hepatoma cell) were also concordant with those in the toxicity tests. Significant liner relationships (p<0.01) were found between GSH contents in the rat hepatoma cells and PAHs, OCPs contents in the sediment extracts. It is recommended that the present suite of bioassays is useful and is biologically relevant for future ecotoxicological studies focusing on similar wetlands.