Bioactive glasses (BAGs) are bone substitutes with bone bonding, angiogenesis promoting and antibacterial properties. The bioactive process leading to bone bonding has been described as a sequence of reactions in the glass and at its surface. Implantation of the glass is followed by a rapid exchange of Na+ in the glass with H+ and H3O+ from the surrounding tissue, leading to the formation of silanol (SiOH) groups at the glass surface. Due to migration of Ca2+ and PO43− groups to the surface and cystallization, a CaO-P2O5 hydroxyapatite (HA) layer is formed on top of the Si-rich layer. Finally, cell interactions with the HA layer subsequently initiate the bone forming pathway. The rapid increase in pH and the subsequent osmotic effect caused by dissolution of the glass have been suggested to partly explain the antibacterial properties observed for BAGs. Comparing bactericidal effects of different BAGs, BAG-S53P4 has been shown to be the most effective, with the fastest killing or growth inhibitory effect. This antibacterial effect has been observed in vitro for all pathogens tested, including the most important aerobic and anaerobic pathogens, as well as very resistant bacteria. In a multicentre study in 2007–2009, BAG-S53P4 was used as bone graft substitute in treatment of osteomyelitis. Eleven patients (nine males, two females) with a radiologically diagnosed osteomyelitis in the lower extremity (N=10) and in the spine (N-1) participated. In the operation, the infected bone and the soft tissue were removed, and the cavitary bone defects were filled with BAG-S53P4 (BonAlive™, Bonalive Biomaterials Ltd., Finland). In four patients, muscle flaps were used as part of the treatment. Eight patients were treated in a one-stage procedure. Kanamycin granules were used in one patient and Garamycin granules (Septocol ®) in two patients. Patient data were obtained from hospital patient' records until August 2010, resulting in a mean follow-up period of 29 months (range 15–43). BAG-S53P4 was well tolerated; no BAG-related adverse effects were seen in any patient. The use of BAG-S53P4 as a bone graft substitute resulted in a fast recovery. Long-term clinical outcome was good or excellent in ten of eleven patients. These primary results indicate that BAG-S53P4 can be considered as a good and usable material in treatment of osteomyelitis. After this study BAG-S53P4 has been used in several other patients with very promising results