Propolis is a natural product that is collected by the honeybee (Apis mellifera L.) from plants. The in vitro genotoxic potential of propolis in human lymphocytes was investigated. Blood samples were obtained from ten healthy (five female and five male), non-smoking and alcohol volunteers, which were incubated and exposed to increasing concentrations of propolis (5, 25, 50 and 250 mg/ml). The mean sister chromatid exchange (SCE) rates were 10.398 +/- 1.47-21.522 +/- 2.08. The differences between the control and exposed cells were statistically significant (p < 0.05). Increasing SCE rates showed that propolis could have genotoxic effects in high concentrations. SCE rates of women donors exceeded those of men donors. Women donors had the highest SCE rates (25.674 +/- 8.71, 22.456 +/- 7.97 and 15.756 +/- 5.09 for mean of SCE).