Essential oil extracted by hydrodistillation from Rosmarinus o cinalis was characterized by means GC-MS. R. o cinalis contained α-pinene, β-pinene, eucalyptol, camphor and caryophyllene, respectively, as the major compounds. An adapted difussion method was used in order to assess the potentiator effect of the essential oil and the analytical standard (eucalyptol) on the antibiotic susceptibility of S. aureus strains to some of the currently used antibiotics, i.e. tetracycline, oxacillin, erythromycin, penicillin, cefoxitin, doxycycline as well as suphametoxazole. Five S. aureus strains were tested, four of clinical origin (two wound secretions and two blood cultures) and one reference strain, i.e. S. aureus ATCC 25923. The R. o cinalis essential oil and its main constituent, eucalyptol, exhibited a strong, strain specific influence on the antibiotic susceptibility of the tested strains.