Cyanobacteria and microphytic algae (23 species), including toxic water bloom stimuli in Ukrainian waters and Black Sea coastal region were tested on some injurious organisms of different evolutionary level. As a result antibacterial, antihelminthic, deterrent and insecticidal characteristics of a number of cyanobacterial and microalgal (Dinophyta, Chlorophyta and Xanthophyta) species and strains as well as their natural associations can be ascertained. The most perspective variants of their application in medical and agricultural practice may be considered as selective and prophylactic means, and new biological preparations would be created on this base. Cyanobacteria and microalgae have displayed inhibitory action on vital functions (nutrition, growth, metamorphosis and reproduction) of some herbivorous insects ˆ Colorado potato beetle, fall webworm, lackey, gypsy, brown-tail and ermine moths. Their larval phases (especially junior instars) were the most susceptible to the action of algal metabolites, so the main part of insects (70.0-100.0%) was eliminated during these stages. The mortality of the following larval instars, pupae and imago was not so high, but metatoxic effect took place there. So a number of insects (for example, Colorado potato beetle) in natural communities was decreased because of a total mortality in all of phases (89.3-97.4%) and degradation of the second pest generation in 22.8-62.7% (in control variant without treatment this index increased in 717.3%). Applicable concentrations and doses of these new preparations did not bring any damage to the plants, entomophagans (coccinellids and carabids) and warm-blooded animals. Their biological activity and protective efficiency can be comparable with well-known microbial insecticides, and in some cases they are more preferable. In particular, it is very difficult for terrestrial organisms to be resistant to non-typical substances. There are several ways to obtain cyanobacterial and microalgal biomass for the practical employment. Some of them can use a natural material from harmful species with its subsequent treatment. Controlled methods of cultivation or sewage utilization in cattle-breeding complexes for nutrient substratum are acceptable for this purpose too.