Black pepper is a spice widely used in human food. The aim of this investigation was to determine whether an alcoholic extract of the mature berries of black pepper induced genotoxic damage in vivo and in vitro. The first aspect was evaluated in mouse bone marrow cells and the second one in human lymphocytes. In both cases the rate of sister chromatid exchange (SCE) and the replicative index were determined. For the in vivo assay, ip doses of 7.0, 14.0, 28.0 and 56.0 mg/kg body weight were tested, with the following results: (1) a significant increase of SCE frequency in all doses tested compared with the control level (the highest dose produced almost a duplication of the basal rate of SCEs); (2) a similar pattern with regard to cell proliferation kinetics at all doses tested, without significant differences between them. For the in vitro assay, doses of 25.0, 50.0, 75.0 and 100.0 micrograms/ml were tested, with the following results: (1) a significant increase in the frequency of SCEs at all doses tested; a linear regression analysis of the data produced a correlation coefficient of 0.98; (2) a significant reduction in the replicative index, at the two high doses. These results demonstrated that the extract of black pepper was genotoxic in both systems.