Experiments were directed towards the detection of slight alterations to the biochem. organization of the liver cell caused by diverse compounds possessing very different toxicities.Untreated rats were compared with rats treated with the hepatotoxic compoundsCCl4, safrole, allyl alc., coumarin, β-thujone, ethionine, thioacetamide, 3-methyl-4'-dimethylaminoazobenzene, dimethylnitrosamine and aflatoxin; food additives such as butylated hydroxyanisole, butylated hydroxytoluene, and sucroglyceride; stabilizers as dioctyltin and 2-phenylindole; drugs such as Drazine and Na barbitone and other compounds such as Triton X-100 and Me2SO.A significant reduction in glucose-6-phosphatase activity was observed when any of the hepatotoxic compounds was administered in appropriate dose levels and for appropriate lengths of time.Similarly, 2-phenylindole and butylated hydroxytoluene when given in high dose brought about a decrease in the activity of this enzyme.The other compounds did not cause any significant reduction of glucose-6-phosphatase.Glucose-6-phosphate dehydrogenase activity was increased after treatment of rats with CCl4, coumarin, ethionine, dimethylnitrosamine, 2-phenylindole, and high doses of butylated hydroxytoluene.Changes in the activity of the lysosomal enzymes tested did not run parallel, and after the administration of hepatotoxic compounds, acid phosphatase and arylsulfatase were increased, whereas β-glucuronidase and cathepsin did not show a marked change.Na barbitone treatment did not result in any change of the liposomal enzymes and no difference was found in the activity of succinic dehydrogenase in liver mitochondria of rats treated with various compounds