The combined action of fosfomycin with penicillin G, ampicillin and streptomycin was investigated. A total of 11 S. aureus and 10 E. coli were included in these studies. It has been shown that a combination of fosfomycin with penicillin G and streptomycin resulted in a synergistic effect. When S. aureus strains were tested, the combination of fosfomycin with penicillin G was more frequently effective than the combination of fosfomycin with streptomycin. The combination of fosfomycin with ampicillin and streptomycin showed a similar synergistic effect on 7 of 10 E. coli strains. The antagonistic effect never resulted when the above-mentioned combination of antibiotics were used. The authors postulate that a combination of fosfomycin with β-lactam or aminoglycoside antibiotics may be used in clinical practice and such a procedure should prevent an emergence of fosfomycin-resistant strains