The importance of chemoprevention is increasing nowadays because these substances have important biological effects, e.g. anti-inflammatory, immunomodulating and immunostimulating, they influence blond pressure regulation, blond sugar and cholesterol levels. Their anticancerogenic effects are also important as nowadays with regard to the type of tumourous disease it is assumed that by chemoprevention it is possible to restrict the development of new oncological diseases within a range of 30 - 60 %.The large number of oncological patients in the Czech Republic (260 000 in 1997) is associated also with an adverse incidence (58 000 in 1997).By application of findings of chemoprevention by dietary habits of the population the number of patients could be markedly reduced. A realistic assumption for our country is a reduction by at least 12 000 - 16 000 of netyly diagnosed cases per year If it esere possible to apply the outlined recommendations on a worldwide scale every year the prevalence of oncological diseases would decline by 3 - 5 million cases.

        Key words: : Chemoprevention - Oncology - Oncological diseases