Ecologically relevant threshold concentrations for antimony are required in order to assess the potential risks of anthropogenic emissions of Sb to the environment. The present paper reports a summary of the ecotoxicity data available for various Sb substances and discusses the derivation of ecological threshold concentrations for Sb in freshwater and soils. It was concluded that data from tests with SbCl3 are useful for calculation of Sb toxicity thresholds in water. The results from SbCl3 in soil toxicity tests have little relevance because of demonstrated confounding factors of pH and salinity. The derivation of Sb threshold concentrations in soil was, therefore, based on toxicity tests in soils amended with the sparingly soluble Sb2O3 with correction for incomplete dissolution during the duration of the toxicity tests. The lowest chronic toxicity thresholds are 1.1 mg Sb L-1 in water and 370 mg Sb kg(-1) dry weight for soil. These concentrations are more than 100-fold larger than typical natural background concentrations.