Marine phytoplankton Porphyridium sp. produced and secreted a mucilaginous polysaccharide in the incubation medium. The polysaccharide production was enhanced by the addition of slag at proper concentration. This polysaccharide showed a moderate mitogen activity, similar to dextran sulfate but lower than concanavalin A and lipopolysaccharide. Polysaccharide was found to have antitumor activity against Sarcoma 180 inoculated in the peritoneal cavity of ddY mice.
