Antagonism or double zones of inhibition (or both) resulted when Staphylococcus aureus was exposed to fosfomycin in Brain Heart Infusion, tryptic/papaic digest of casein/soybean, and Mueller Hinton culture media; neither occurred with a totally defined, completely synthetic medium. The extent of antagonism was quantitated by determination of the absolute minimal inhibitory concentration of fosfomycin in each medium. By using the synthetic medium and inducers, the hexose-phosphate transport system appeared to be more important than the alpha-glycerophosphate transport system in providing ingress of fosfomycin into staphylococci.