Chemoprevention means prevention of cancer by administering chemical compounds. Ideal chemopreventive agents are non-toxic, inexpensive and can be taken orally. A large number of natural and synthetic compounds have cancer preventive properties in cell culture or animal model studies. With the demonstration of tamoxifen's ability to prevent breast cancer in women, the feasibility of chemoprevention in humans has now been firmly established. Current challenge is to build on this success and identify non-toxic chemopreventive agents. A promising area of research is clinical studies with botanicals, cancer preventive compounds in fruits, vegetables and other plants.