Some mycotoxins produced by microfungi are capable of causing disease and death in animals and humans. In the present study, the mycotoxin citrinin (CTN) was evaluated for its genotoxic effects to human peripheral blood lymphocytes from six different individuals. Lymphocyte cultures were treated for 48 h with CTN at six different concentrations between 10 and 100 mu M. Lymphocyte cultures were also incubated with 0.1 mu M mitomycin c (MMC) as a positive control, and 0.5% absolute ethanol as a vehicle control. CTN caused a significant concentration-dependent increase in micronucleus (MN) frequency in human lymphocytes. At the 60 mu M, 80 mu M and 100 mu M concentrations, CTN was found to induce MN in cytokinesis-blocked lymphocytes in comparison with negative controls (P = 0.014). All the CTN concentrations also led to a clear decrease in the percentages of binucleated/mononucleated cells (P = 0.014). These results indicate that CTN at high concentrations is genotoxic in cultured human lymphocytes. Copyright (C) 2007 John Wiley & Sons, Ltd.