Background: Staphylococcus aureus bacteraemia is a common and frequently fatal infection. Adjunctive rifampicin may enhance early S. aureus killing, sterilise infected foci and blood faster, and thereby reduce the risk of dissemination, metastatic infection and death. Objectives: To determine whether or not adjunctive rifampicin reduces bacteriological (microbiologically confirmed) failure/recurrence or death through 12 weeks from randomisation. Secondary objectives included evaluating the impact of rifampicin on all-cause mortality, clinically defined failure/recurrence or death, toxicity, resistance emergence, and duration of bacteraemia; and assessing the cost-effectiveness of rifampicin. Design: Parallel-group, randomised (1 : 1), blinded, placebo-controlled multicentre trial. Setting: UK NHS trust hospitals. Participants: Adult inpatients (≥ 18 years) with meticillin-resistant or susceptible S. aureus grown from one or more blood cultures, who had received