Chemoprevention by extracts of Laurencia obtusa (E1) and Caulerpa prolifera (E2) collected from the Egyptian coast of the Red Sea against aflatoxin B1 (AFB1)-initiated hepatotoxicity in female Sprague-Dawley rats has been studied. Animals were fed aflatoxin-contaminated diet (3 mg kg−1 diet) for 6 days then treated orally with pure aflatoxin B1 (AFB1) (200 µg kg−1 b.w.) for 4 days either in combination with or before E1 or E2 administration (50 mg kg−1 b.w.). AFB1 resulted in a signicant increase in serum alpha fetoprotein, carcinoembryonic antigen, tumor necrosis factor alpha, nitric oxide, interleukin-1α, procollagen III and lipid peroxidation level in the liver. It caused a signicant decrease in food intake, body weight, serum leptin, the activities of glutathione peroxidase, superoxide dismutase and DNA and RNA concentrations in the liver. Cotreatment with AFB1 and E1 or E2 resulted in an obvious improvement in all tested parameters. Noteworthy, E2 was more effective than E1 in the protection against AFB1-induced hepatotoxicity. Copyright © 2006 John Wiley & Sons, Ltd.