Moderate beer consumption can be considered as part of a healthy diet since it may protect against heart disease, cancer and osteoporosis. The protective effects of beer reside in its polyphenol content whose chemical composition appears extremely complex. In the present study, five commercial beers with different polyphenol content (ranging between 690 - 2400 μM equivalents of quercetin) were employed to investigate their cytotoxic effect in vitro on HL-60 cells derived from a human promyelocytic leukemia cell line. A significant reduction in cell viability was measured after 48 hours treatment. Lyophilized beers with higher polyphenol content showed the highest cytotoxicity compared to those with lower concentrations. However, when the assay was performed applying equal amounts of total polyphenols from different lyophilized beers, the sample possessing lowest amount of polyphenols (690 μM equivalents of quercetin) resulted the most effective in reducing cell viability. These data suggest that the biological activities of polyphenols present in beer are not simply dependent upon their total concentration, but qualitative profile and relative concentrations are even more important in determining their antiproliferative effects on cancer cells.