MIC and MBC values of ofloxacin and ceftriaxone were investigated against Staphylococcus aureus in MHB and MHB containing additional Mg²⁺, Al³⁺, Fe³⁺, Ca²⁺, Zn²⁺, Cu²⁺. The addition of Mg²⁺, Al³⁺, Fe³⁺ increased the MIC and MBC of ofloxacin and the MBC of ceftriaxone. However, the addition of these cations did not change the MIC of ceftriaxone. Our findings suggest that these interactions might be due to the formation of chelates between metal ions and antibiotics. These results also indicate that some cations may have an important role in the antibacterial activity of antibiotics.