Seventy one species of marine macrophytes from the Central Mediterranean have been screened for the production of antibacterial, antifungal, antiviral, cytotoxic and antimitotic compounds. Sixty five of the species displayed some kind of activity and most of them were active on more than one organism or cell tested. Antifungal activity was the most widespread (70% of the plants), whilst the incidence of antibacterial activity was extraordinarily low (6% of the plants). Of the plants tested 21% showed antiviral activity, 35% were cytotoxic and nearly 50% had antimitotic properties. The maximum level of activity was found among the Chlorophyta; some members of the Bryopsidales (Flabellia petiolata, Caulerpa prolifera, Halimeda tuna) were the most active species. Most of the dominant species in Mediterranean phytobenthic communities