Ochratoxin A (OTA), a nephrotoxic and carcinogenic mycotoxin, was investigated to examine its potency to induce micronuclei (MN) in cultured human lymphocytes. Lymphocyte cultures were treated for the last 48 h with OTA at concentrations of 25 mum, 10 mum, 1 mum, 100 nm, 10 nm, 1 nm, and 100 pm and absolute ethanol. At the highest concentration, OTA was found to induce MN in cytokinesis-blocked lymphocytes (p < 0.05). The 25 muM OTA concentration also led to a clear decrease in the percentage of binucleated cells, probably due to cytotoxicity. OTA at the other concentrations tested did not induce MN frequency. These results indicate that a high concentration of OTA is genotoxic in cultured human lymphocytes.