Allicin is one of the most effective compounds isolated from garlic showing antibacterial activity. Determination of MIC alone or in combination with cefazolin/oxacillin against Staphylococcus spp. or with cefoperazone against Pseudomonas aeruginosa showed that allicin alone did not have good antibacterial activity (MIC90>512 microg/ml) but it facilitated antibacterial activity of all three beta-lactams tested at subinhibitory concentrations. In the presence of 1/8 to 1/2 the MIC of allicin, the MIC90 values of cefazolin, oxicillin, and cefoperazone were reduced by 4 approximately 128, 32 approximately 64, and 8 approximately 16 fold, respectively. Thus, allicin-beta-lactam combinations offer promise of clinical utility especially if synergism is demonstrated by in vivo experimental studies.