In recent years, awareness of the problem of human and animal exposure to potentially toxic chemicals in our environment has grown. Perhaps one of the first to bring this to the attention of the public was Rachel Carson with her book Silent spring. This was a description of the devastating effects of pesticides on the flora and fauna of the North American environment. As discussed by Efron in her book The Apocalyptic. Cancer and the Big Lie (1984), Carson and certain later scientists probably exaggerated the dangers of chemicals, but her massage was quite clear. Few would disagree that man should be aware of the synthetic chemicals to which the environment is exposed. thus, toxicology has another dimension: the social, moral and legal aspects of exposure of populations to chemicals of unknown or uncertain hazard. Hazard and risk assessments and value judgments become important. The toxicologist is often asked to make such assessments and judgments. So toxicology has a very important role to play in modern society and consequently it is now growing rapidly as a new subject.