In this single-arm non-comparative trial, 13 patients in an Australian hospital with severe Staphylococcus aureus infections were intravenously administered a good manufacturing practice-quality preparation of three Myoviridae bacteriophages (AB-SA01) as adjunctive therapy. AB-SA01 was intravenously administered twice daily for 14 d and the clinical, haematological and blood biochemical parameters of the recipients were monitored for 90 d. The primary outcome was the assessment of safety and tolerability (that is, pain and redness at the infusion site and systemic adverse reactions, such as fever, tachycardia, hypotension, diarrhoea or abdominal pain and the development of renal or hepatic dysfunction). No adverse reactions were reported, and our data indicate that AB-SA01 administered in this way is safe in severe S. aureus infections, including infective endocarditis and septic shock. Future controlled trials will be needed to determine the efficacy of AB-SA01 but no phage resistance evolved in vivo and the measurements of bacterial and phage kinetics in blood samples suggest that 12 h dosing of 109 plaque-forming units may be a rational basis for further studies.