Biotoxicity tests are considered methods to assess toxicity of substances or complex mixtures of industrial wastewater effluents. In this study, Daphnia similis and Cyprinus carpio were used to examine the acute toxicity of thin-film transistor liquid crystal display (TFT-LCD) wastewater effluents in Taiwan. Among examined effluents, 67% were found to be toxic to D. similis and 27% were toxic to C. carpio. The biotoxicity of TFT-LCD wastewater effluents might be due to the presence of tetra-methyl ammonium hydroxide (TMAH), since 48-h lethal concentration 50 (LC50) of TMAH to D. similis was found only 0.75 mg/L. The acute toxicity of NH4+-N to D. similis varied with 48-h LC50 values of 18.5 mg/L at pH 7.0 and 155 mg/L at pH 6.5. The obtained results of this study indicated that NO3--N, SO42-, Cl- and heavy metals were not the major concerns in TFT-LCD wastewater effluents regarding acute toxicity. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.