The genotoxic effect of a 100 Hz pulsed magnetic field (PMF) in human peripheral blood lymphocyte cultures from 25 healthy subjects was investigated. For this purpose, the cytokinesis-block micronucleus assay (MN), using two concentrations of cytochalasin-B (Cyt-B; 3 and 6 μg ml - 1 ), was applied to evaluate the micronucleus frequency in unexposed and PMF-exposed cultures obtained from blood of the same subjects. Cell proliferation was also evaluated applying the cytokinesis-block proliferation index (CBPI), which indicates the average number of cell cycles undergone by a given cell.The results obtained indicate that, under the experimental conditions used in this study, 72 h 100 Hz PMF exposure produced a statistically significant increase of both MN and CBPI in exposed cultures with respect to unexposed ones, at variance with previous results showing no genotoxic effects with 50 Hz pulsed magnetic fields, used for therapeutic bone repair.