Farnesol, a sesquiterpene alcohol, potentiates the activity of β-lactam antibiotics against antibiotic-resistant bacteria. We document that farnesol and two synthetic derivatives (compounds 2 and 6) have poor antibacterial activities of their own, but they potentiate the activities of ampicillin and oxacillin against Staphylococcus aureus strains (including methicillin-resistant S. aureus). These compounds attenuate the rate of growth of bacteria, which has to be taken into account in assessment of the potentiation effect.