An experimental and theoretical study was performed on the anti-staphylococcal activity of 18 natural and synthetic #avonoids against methicillin-resistant Staphylococcus aureus strains. The analysed #avonoids belong to three well-di!erentiated structural patterns: chalcones, #avanones and #avones. The quantitative analysis of the anti-staphylococcal activity of the compounds was carried out by determining their percent inhibition degree. The hierarchical cluster analysis method was used to analyse the anti-MRSA activity of the compounds. With this methodology, the #avonoids were classi"ed into four groups according to their antistaphylococcal activity (high, su$cient, intermediate and low). The carbonylic region is of importance because it is part of the bioactive region inducing anti-MRSA activity in the #avonoid molecules. The introduction of OH groups in positions 2 of chalcones and 5 of #avanones (or #avones) increases #avonoid activity, while the OCH groups produce the reverse e!ect. Using the experimental anti-MRSA activity data of #avonoids and six quantum chemical parameters calculated by means of the AM1 semiempirical molecular orbital method, a very good quantitative structure}activity relationship was obtained (con"dence range: 95%; signi"cance level for tests: 0.05; correlation coe$cient"0.9842). The selected parameters explain 96.86% of the percent inhibition degree. The obtained relation is consistent with the conclusions formulated in this paper and serves as a theoretical support for some of them. Finally, it is concluded that the #avonoids chalcone, 2(OH)-chalcone, 2,4(OH) -chalcone and 2,4(OH)
-chalcone might constitute promising therapeutic agents against infections with methicillin-resistant S. aureus strains.