Mesopelagic organisms form huge biomass aggregations, supporting important pelagic trophic webs and several top predators. Although some studies on the occurrence, biology and ecology of these organisms are available, to date there are no investigations on their potential use for anticancer and antimicrobial biotechnological applications. The aim of this study was to screen extracts of seven mesopelagic species for possible anticancer (Lung cell line A549, skin cell line A2058, liver cell line HepG2, breast cell line MCF7 and pancreas cell line MiaPaca-2) and antibacterial (Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae, the Gram-positive bacteria methicillin resistant/ sensitive Staphylococcus aureus, and Mycobacterium tuberculosis) activities. Results showed that only two species were active, the lanternfish Myctophum punctatum and the Mediterranean krill Meganyctiphanes norvegica. In particular, M. punctatum showed strong activity against the A549 and MCF7 cells, while M. norvegica was more active against HepG2 cells. Regarding antibacterial assays, both species were active against methicillin resistant S. aureus. Fractionation and LC/MS dereplication of the fractions showed that the main compounds found in extracts of both species were EPA, DHA and ETA. For some of the detected compounds anticancer and/or antibacterial activity are already known, but this is the first time that such activities have been found for mesopelagic species. The mesopelagic zone, from "meso" meaning intermediate, represents a water layer of the ocean below the epipelagic and above the bathypelagic zones, at depths between 200 and 1000 m, that is characterized by increased hydrostatic pressure, diminished light, high inorganic nutrient concentrations and episodic food supply 1. A large number of marine organisms live in the mesopelagic zone, from bacteria to zooplankton and nekton, including species adapted to peculiar conditions, such as the twilight environment, inhabited by a myriad of bioluminescent and unique organisms 2-4. These organisms often form huge biomass aggregations, supporting important pelagic trophic webs and several top predators 5-8. In particular, due to their high density and wide diffusion, mesopelagic fish can be considered the most abundant vertebrates on earth 9. Studies on mesopelagic micronekton have been mainly focused on their distribution, biology and ecology as well as bioluminescent properties but studies related to their potential biotechnological applications are very rare. The reason is mainly due to high costs for their sampling, often requiring the planning of research cruises, the scarce scientific information on most species, and the very scarce available information on their genomes and transcriptomes. Few mesopelagic species are accidentally caught by fishing gear. However, in the Straits of Messina (central Mediterranean Sea), there is a recurrent phenomenon of stranding of mesopelagic organisms due to several factors. Tidal currents, lunar phases, winds and seasons influen...