Saporin belongs to the family of plant enzymes known as ribosome inactivating proteins (RIPs) for their property to depurinate the major rRNA, thus leading to inactivation of ribosomes. In this work we analyzed the genotoxic effects of saporin, purified from root cultures of Saponaria officinalis, by evaluating micronucleus formation and by the quantitative determination of cytosolic histone-associated DNA fragments. Saporin induces micronuclei formation in cultured human lymphocytes in a dose dependent manner; treated lymphocytes show a decrease in cell viability and a concomitant increase in the apoptotic response evidenced by the appearance of cytosolic oligonucleosomes. On the other hand saporin treatment failed to induce sister-chromatid exchange (SCE) at any of the doses tested.