Retroviruses are a relatively newly recognized group of RNA viruses. Many are associated with malignancies in mammals and the virus that has been identified in cases of acquired immune deficiency syndrome (AIDS) is a retrovirus. Because of the severity of AIDS, it has been placed at the top of the nation's health priorities. Antiviral agents are being sought to treat cases of AIDS and other retroviral infections. In the course of testing marine algae for antiviral activity, it was found that one particular alga showed significant in vitro activity against Friend's leukemia virus, a retrovirus. The goal of the proposed research is to determine if this activity will be useful to treat retrovirus-associated disease in humans. The objectives of the Phase I research are to establish the nature and magnitude of the antiviral activity of this alga by using several in vitro assays. In addition, the active agent(s) will be purified and identified. The first stages of this work will involve determining what type of compound is responsible for this activity and then separating it from the crude algal extracts. Characterization of the agent(s) involved will also provide information useful in hypothesizing a mechanism of action.