Exposure of HeLa cells to 0, 5, 10, 25, 50 and 100 microg/ml of guduchi extracts (methanol, aqueous and methylene chloride) resulted in a dose-dependent but significant increase in cell killing, when compared to non-drug-treated controls. The effects of methanol and aqueous extracts were almost identical. However, methylene chloride extract enhanced the cell killing effect by 2.8- and 6.8-fold when compared either to methanol or aqueous extract at 50 and 100 microg/ml, respectively. Conversely, the frequency of micronuclei increased in a concentration-dependent manner in guduchi-treated groups and this increase in the frequency of micronuclei was significantly higher than the non-drug-treated control cultures and also with respect to 5 microg/ml guduchi extract-treated cultures, at the rest of the concentrations evaluated. Furthermore, the micronuclei formation was higher in the methylene chloride extract-treated group than in the other two groups. The dose response relationship for all three extracts evaluated was linear quadratic. The effect of guduchi extracts was comparable or better than doxorubicin treatment. The micronuclei induction was correlated with the surviving fraction of cells and the correlation between cell survival and micronuclei induction was found to be linear quadratic. Our results demonstrate that guduchi killed the cells very effectively in vitro and deserves attention as an antineoplastic agent.