Recently, some countries have focused on the available ultilization of marine resources. This has resulted in the occurrence of food poisoning incidents casused by marine toxins and the development of ew biochemical resources such as drugs and pharmacological reagents. In Taiwan, tetrodotoxin, paralytic shellfish poison and ciguateric toxins are well known as notorious agents to induce severe food poioning. But other causative agents including diarrhetic shellfish poison, domoic acid, brevetoxin and eosurugatoxin have occasionally occurred in other countries. Some agents including laminine, kainiccid, holotoxin and nereistoxin have long been applied as useful drugs. Meanwhile, attempts have reently made to develop useful druges by screening marine organisms for pharmacologically active subances, e.g., antitumor, antibacterial, hemolytic, analgetic, antispasmodic, hypotensive and hypertenve agents. Among them, some of the substances possessing antitumor activities are selectively disnssed in this review.