In the present study the antioxidant activities exhibited by the crude extracts of six marine algae collected from the Aegean Sea shores of Turkey were examined: Padina pavonica, Cystoseira barbata, and Sargassum acinarium of the Phaeophyceae (brown algae), Caulerpa racemosa var. cylindracea of the Bryopsidophyceae (green algae), and Jania longifurca and Laurencia obtusa belonging to the Rhodophyceae (red algae). Antioxidant activities were assessed by measurement of glutathion peroxidase activity spectrophotometrically and malondialdehyde measurement for lipid peroxidation by HPLC. Among the species examined, the highest antioxidative capacity according to specific glutathion peroxidase activity was measured from the extract of the brown alga Sargassum acinarium (124 U/mg protein) followed by another brown alga Padina pavonica (16.20 U/mg protein). Malondialdehyde contents of extracts as an indicator of lipid peroxidation were compared, and S. acinarium extract had the lowest MDA level (0.229 mu mol/l). Antimicrobial activities of the methanolic extracts of P. pavonica, Cy. barbata, S. acinarium and J. longifurca were also evaluated against eight microorganisms (7 bacteria and a yeast strain). The extracts showed moderate inhibitory activity
