The effects of various concentrations (0.0, 1.56, 3.125, 6.25, 12.5, 25, 50 and 100 mug/ml) of the leaf extract of Syzygium cumini Linn. or Eugenia cumini (SC; black plum, Jamun, family Myrtaceae) was studied on the alteration in the radiation-induced micronuclei formation in the cultured human peripheral blood lymphocytes. Treatment of lymphocytes to various concentrations of SC resulted in a dose dependent increase in the micronuclei-induction, especially after 25-100 mug/ml extract. The exposure of human lymphocytes to various concentrations of SC extract before 3 Gy gamma-irradiation resulted in a significant decline in the micronuclei-induction at all the drug doses when compared with the non-drug treated irradiated cultures. A nadir in MNBNC frequency was observed for 12.5 mug/ml drug concentration, where the MNBNC frequency was approximately fourfold lower than that of the non-drug treated irradiated cultures. Therefore, this dose may be considered as an optimum dose for radiation protection. Our study demonstrates that the leaf extract of S. cumini, a plant traditionally used to treat diabetic disorders protects against the radiation-induced DNA damage. (C) 2002 Published by Elsevier Science Ireland Ltd.