Green tea is the second-most consumed beverage in the world (water is the first one) and has been used medicinally for centuries in Indiaand China. The active substances in the green tea are polyphenols (catechins) and flavonols which possess a potent antioxidant activity. Epigallocatechin gallate (EGCG) is one of the four major green tea catechins. Using the Ames test, micronucleus test, comet assay, chemiluminescence test, and blastic transformation test, we examined the antimutagenic effects of chemoprotective substance epigallocatechin gallate (EGCG) in the pure form on the mutagenicity induced by three reference mutagens: aflatoxin B₁ (AFB₁), 2-amino-3-methylimidazo [4,5-f] qui-noline (IQ), and N-nitroso-N-methylurea (MNU), and the effect of EGCG on the immunosuppression caused by these mutagens. Using the Ames test the dose dependent antimutagenic activity of EGCG was proved against indirect mutagens AFB₁ and IQ, but not against the direct mutagen MNU. In the micronucleus test, EGCG had antimutagenic effect upon all three mutagens. EGCG decreased the level of DNA breaks induced by AFB₁ in bone marrow cells and colon epithelium, and the level of DNA breaks induced by MNU in colon cells to the level found in control. The reparatory effect of EGCG on immunosupression induced by all three carcinogenic compounds was proved using chemiluminescence and blastic trasformation tests.