Praziquantel, a drug used for the treatment of neurocysticercosis, was tested for its ability to induce morphological transformation of Syrian hamster embryo fibroblasts. Results indicate that praziquantel transforms these cells without affecting their viability. Further experiments were carried out to investigate its possible mechanism of action in the same cell system. Micronucleus formation was observed in cultures treated with concentrations which induced morphological transformation, about 40% of these micronuclei were positive to a kinetochore antibody. No induction of DNA repair synthesis was observed even at cytotoxic concentrations. These results suggest that praziquantel has an aneugenic effect which could be responsible for its ability to transform morphologically these cells. Risk-benefit analysis should be carried out whenever this drug is utilized.