The marine environment is a prolific resource for the isolation of less exploited microorganisms. As a matter of fact, in the sea, untapped habitats exist with unique characteristics. In addition, the potential contribution of marine sources to the discovery of new bioactive molecules was recently recognized. Biosearch Italia possesses a collection of about 40000 microorganisms, isolated from different ecological niches. In the search of new bioactive entities, investigations were expanded to marine habitats including marine sediments and organisms. More then 800 microorganisms have been isolated. About half belong to fungal genera, the others being actinomycetes. The frequency of antibiotic activities produced by these marine strains has been determined. Initial data are encouraging: marine isolates produce antibiotic activities with frequencies comparable to terrestrial ones. These activities probably represent a mixture of novel metabolites and known products previously discovered from terrestrial isolates. Further investigations are ongoing to assess the novelty of these observed microbiological activities. (C) 1999 Elsevier Science B.V. All rights reserved.