The article presents a survey of biotests and their application in environmental analysis. Attention is directed towards a bacterial bioluminiscence toxicity test (Microtox test) which exhibits a number of advantages in comparison with the other biotests. The factors and sources of errors are discussed which affect the correctness of the results as well as some of its advantages. Its use in the detection of acute toxicity of substances is also assessed where the state of health of the testing organisms is damaged. This plays an important role in environmental protection.