The diversity, biological activity and secondary metabolite production of fungi associated with marine sponges were investigated in order to assess the potential of these fungi for the production of novel biologically active secondary metabolites. 681 fungal strains were isolated from 16 sponge species from six different locations, representing 13 genera of Ascomycota, 2 of Zygomycota, 37 of mitosporic fungi, and 37 strains of sterile mycelium. The spectrum of fungi from each location was dominated by a few genera of mainly mitosporic fungi that are also commonly encountered in terrestrial habitats.

A high proportion of culture extracts of sponge-associated fungi was biologically active in tests to detect antifungal, antialgal, and antibacterial activity, cytotoxicity and inhibition of reverse-transcriptase and tyrosine kinase. The corresponding chemistry was structurally diverse and related to that of terrestrial fungi. From the biologically active culture extracts of five fungal strains, nine pure compounds were isolated in addition to 18 previously reported.