Comparing with the trivial physical, physicochemical and chemical ways of the search of the agents of interest, the bioassays have the set of advantages, including the demand of less precision tools, less amounts of costs, labors and some other means. To date bioassays have formed the separate domain with its own theoretical basis, including classification, systematization, methodology, and meta-research. The present review analyzes the major spheres of the application of bioassays, such as environmental monitoring, quality control of foods. Bioassays contribute to the studies of the properties of plant metabolites, the peculiarities of the influence of various agents with potentials of toxicity, genotoxicity, neurotoxicity, mutagenicity, teratogenicity, endocrine disruption, etc. Bioassays not only enable the identification of stimuli by the specificity of structure (from atomic to supramolecular level), but also explore the stimuli functionally – in sense of the diversity of biological effects. This research approach is built on the indicators, which belong to the vast range of levels of living matter: from macromolecules to multi-cellular organisms. Great attention in this paper is paid to the parameters, detected in the process of bioassays, also to the methods and related instruments. We divide the methods into general physical, general chemical, general biologic and complex ones. The series of challenges to be researched in future are highlighted. They are: 1) elaboration of the investigatory option, which would be the same with the quantitative tests in chemistry; 2) the integration of the ideas of conventional bioassays with the ideas of bioindication and biolocation; 3) extension of the knowledge about correlation of distinct biological effects, induced by stimuli. Ultimately, bioassays are proved to be the actively developing domain of knowledge.