Two combined antibiotic treatments were compared in 35 cases of methicillin-sensitive Staph. aureus infection. Eighteen patients (including 17 with septicaemia) received penicillin M (methicillin or oxacillin) and gentamicin daily for a mean period of 11 days. Clinical and bacteriological cure was obtained in 14 cases; 2 of these 14 patients developed superinfection with gentamicin-resistant enterobacteria, 1 relapsed and 2 had renal impairment. Seventeen patients (including 15 with septicaemia) were given fosfomycin and penicillin M for a mean period of 17 days. Clinical and bacteriological cure was obtained in 16 patients; the patient with clinical and bacteriological failure died. There was no superinfection or relapse; 3 patients had hypokalaemia and 1 had renal damage caused by methicillin. The clinical and bacteriological results, therefore, were in favour of the fosfomycin-methicillin combination, but the only statistically significant difference between the two groups concerned the complications.