Mycotoxins are fungal secondary metabolites that can be found in contaminated food and feed. There is some evidence to suggest that certain mycotoxins may be mutagenic. Here, we investigate the genotoxicity of the mycotoxin moniliformin (MON) (3-hydroxycyclobut-3-ene-1,2-dione) in human peripheral blood lymphocytes using chromosomal aberration (CA), sister-chromatid exchange (SCE), and micronucleus (MN) analysis. Lymphocyte cultures were treated for 48 h with six different concentrations of MON between 2.5 and 25 mu M. CA, SCE, and MN frequencies were significantly increased in a dose-dependent manner compared with the negative control. The mitotic, replication, and cytokinesis-block proliferation indices were not affected by treatment with MON. The results provide evidence to demonstrate that MON can exert cytogenetic effects in human cells in culture. Environ. Mal. Mutagen. 50:431-434, 2009. (C) 2009 Wiley-Liss, Inc.