Evaluation of genotoxic effects of potassium chromate (K 2 CrO 4 ) and cadmium chloride (CdCl 2 ) was carried out in human blood lymphocytes in vitro as measured by the electron microscopy in situ end-labeling (EM-ISEL). EM-ISEL was used to assess DNA single-strand breaks (SSBs) expressed as number of immunogold particles per μm 2 of chromatin at both chromosomal and nuclear DNA levels. Human lymphocytes were cultured in supplemented RPMI medium for 72h including treatment for 2h with K 2 CrO 4 (0–150μM), CdCl 2 (0–150μM) or methyl methanesulfonate (500μM) as a positive control. Quantification of SSBs by EM-ISEL showed that both compounds are genotoxic agents at non-cytotoxic concentrations. This study brings new information on the utility of EM-ISEL for the evaluation of genotoxicity and confirms the genotoxic effects induced by chromium and cadmium.