Parabens (PBs) are p-hydroxybenzoic acid ester compounds commonly employed as antimicrobial preservatives, mainly in food, cosmetic, and pharmaceutical products. The aim of the present study was to investigate the genotoxic and cytotoxic effects of some paraben esters (butyl paraben, propyl paraben, isobutyl paraben, and isopropyl paraben) on human peripheral lymphocytes, using in vitro sister chromatid exchange (SCE), chromosome aberration (CA), and cytokinesis-block micronucleus (CBMN) tests. Lymphocyte cultures were treated with four concentrations of PBs (100, 50, 25 and 10 mu g/mL) for 24 and 48 h. Paraben esters significantly induced MN formations as compared to solvent control. Furthermore, butyl paraben and propyl paraben increased MN formations a concentration-dependent manner at 24 and 48 h. PBs increased the CA at 24 and 48 h. However, this increase was not meaningful for butyl paraben and isopropyl paraben at 48 h when compared with solvent control. Butyl, isobutyl, and isopropyl paraben significantly increased the SCE at 24 and 48 h. However, propyl paraben did not induce SCE meaningfully in both treatment periods. A significant decrease in the cytokinesis-block proliferation index and mitotic index was observed in cells exposed to all concentrations of PBs at 24 and 48 h. However, proliferation index was not affected at all concentrations of PBs after 24 h treatment, although it was decreased at the highest concentration of PBs at 48 h. It is concluded that all of the paraben esters used in this study have highly genotoxic and cytotoxic effects on human lymphocytes cells in vitro.