Marine products contain arsenic in high concentration compared with other foods. People have eaten many marine products in Japan and have been exposed to many arseniclas. Many of these arsenic compounds are organic and water soluble. To evaluate the risk associated with this intake of arsenic, the toxicological properties of the most common arsenic compounds in marine products must be known. Arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium iodide were examined for cytotoxicity, chromosomal aberration and sister chromatid exchange (SCE) . Arsenobetaine, the major water-solubule organic arsenic compounds contained in many marine animals, exhibited very low toxicity toward mammalian cells. The toxicity of the other arsenic compounds in these tests was lower than the toxicity of arsenite or arsenate.