L-4-Oxalysine hydrochloride is a natural product isolated from the culture media of Streptomyces roseovirdofuscus in China which has shown antitumor activities. In Vitro: Alpha-fetoprotein (AFP) is expressed in BEL-7404 human hepatoma cells and L-4-Oxalysine suppresses AFP mRNA expression in the cells^[1]. L-4-oxalysine functionally antagonizes the a-fetoprotein-induced suppression of the mitogen- and one-way mixed lymphocyte culture-induced proliferation of spleen lymphocytes and interleukin-6 production by these cells in mice bearing the hepatoma-22 tumor^[2]. In Vivo: Tbe ultrastructural efects of different doses of L-4-Oxalysine on hepatocytes in mice are most serious at day 1 after stopping treatment. Mice are given ig L-4-oxalysine (I-677) 10, 50, and 100 mg/kg for 7 d. On day 8 the hepatocytes show accumulation of lipid droplets followed by loss of matrices in cytoplasm. The total area of lipid droplets is far less than 25% of mean section of hepatocytes. The injury of mitochondria and RER is only found in the groups of medium and high dose^[1]. L-4-oxalysine inhibits the proliferation of some mouse implanted tumors and pulmonary metastasis of mouse Lewis lung carcinoma^[2].