Microbial toxicity tests using standardized ISO/OECD methods are crucial for assessing the environmental impact of chemical compounds. These tests help determine the toxicity of substances to microorganisms, which is essential for risk assessment and biodegradation studies. The review highlights the importance of standardized microbial toxicity tests in predicting the effects of chemicals in natural and technical environments. Various standardized tests, such as respiration inhibition, nitrification inhibition, and luminescent bacteria tests, are described, along with their advantages and limitations. These tests are often used in conjunction with biodegradation tests to characterize inocula and assess the potential for microbial adaptation. The concept of physiological potential of an inoculum (PPI) is introduced, which includes chemical resistance potential (CRP) and biodegradation adaptation potential (BAP). The review also discusses the sensitivity and usefulness of these tests compared to other ecotoxicological tests. The importance of microbial toxicity tests in wastewater treatment plants is emphasized, as they help monitor the quality of influent and effluent. The review concludes that while microbial toxicity tests are valuable, they should be used in combination with other tests to provide a comprehensive assessment of chemical toxicity and environmental impact. The integration of microbial and ecotoxicity tests with biodegradation tests offers a promising approach for characterizing chemical compounds and their mixtures.Microbial toxicity tests using standardized ISO/OECD methods are crucial for assessing the environmental impact of chemical compounds. These tests help determine the toxicity of substances to microorganisms, which is essential for risk assessment and biodegradation studies. The review highlights the importance of standardized microbial toxicity tests in predicting the effects of chemicals in natural and technical environments. Various standardized tests, such as respiration inhibition, nitrification inhibition, and luminescent bacteria tests, are described, along with their advantages and limitations. These tests are often used in conjunction with biodegradation tests to characterize inocula and assess the potential for microbial adaptation. The concept of physiological potential of an inoculum (PPI) is introduced, which includes chemical resistance potential (CRP) and biodegradation adaptation potential (BAP). The review also discusses the sensitivity and usefulness of these tests compared to other ecotoxicological tests. The importance of microbial toxicity tests in wastewater treatment plants is emphasized, as they help monitor the quality of influent and effluent. The review concludes that while microbial toxicity tests are valuable, they should be used in combination with other tests to provide a comprehensive assessment of chemical toxicity and environmental impact. The integration of microbial and ecotoxicity tests with biodegradation tests offers a promising approach for characterizing chemical compounds and their mixtures.