The antimicrobial susceptibility of 68 Staphylococcus aureus isolates collected during 2004 from milk of cows affected by subclinical mastitis was examined. The anti- microbial agents tested were the β-lactams, penicillin G, amoxicillin, ampicillin, cloxacillin, amoxicillin + cla- vulanate, cephalonium, and cefoperazone; and other drugs including lincomycin, oxytetracycline, doxycy- cline, and kanamycin. Minimum inhibitory concentra- tions recorded show that only certain β-lactamase–re- sistant penicillins (specifically cloxacillin) or penicillin combinations (amoxicillin + clavulanate) were consis- tently effective against Staph. aureus, whereas the other β-lactam derivatives and drugs from other phar- macological groups were either moderately effective or ineffective. Thus, β-lactamase–resistant penicillins are to be considered the antimicrobial agents of choice for treatment of bovine mastitis resulting from infection by Staph. aureus. Key words: Staphylococcus aureus, bovine, minimum inhibitory concentration