The long-term objective of this part of the proposal is to develop antitumor, antiviral, an antimicrobial drugs from microalgal sources. The proposal is based on the recent findings of the occurrence of promising compounds in dinoflagellates and other microalgae. Anticipated compounds include polyethers, macrolides, other polyoxygenated compounds, cyclic peptides and depsipeptides. There are strong indications that many of the unique metabolites found in marine invertebrates are actually derived from microalgae. The applicant's group has lengthy experience in culturing microalgae and studying their secondary metabolites and is in possession of a vast collection of unexamined microalgal strains. Specifically, l. Free-living dinoflagellates, diatoms, algae in Chrysophyta, and other microalgae from both temperate and tropical waters, and some from freshwater, will be collected, cultured and screened for the bioactivity. 2. Organisms of the above classes symbiotic or associated with marine invertebrates and algae will be isolated, cultured and screened. 3. Active compounds will be isolated, and the structures of the purified compounds will be studied by physico-chemical methods including high field NMR, mass spectroscopy, and X-ray crystallography. Antitumor and antiviral assays and further development of drugs will be conducted by Bristol-Myers Squibb Co., but limited in-house cytotoxicity and antimicrobial tests will be performed as quick isolation guides.