In this study, we benefited from the sensitivity of ion beam analysis methods to characterise in vitro the bioactive glass/biological fluids interface and to perform local measurements of elemental concentrations at the 10 −6 g/g level. A glass in the SiO 2 –CaO composition was elaborated by sol–gel processing. Samples of glass powders were soaked in biological fluids for periods up to 4 days. The surface changes were characterised using particle-induced X-ray emission (PIXE) associated to Rutherford backscattering spectroscopy (RBS), which are efficient methods for multi-elemental analysis. In addition, these ion beam methods permit accurate trace elements quantification. Elemental maps of major and trace elements were obtained at a micrometer scale and revealed the bone-bonding ability of the material. The formation of a calcium phosphate-rich layer occurs after a few minutes of interaction and the glass particles are progressively coated with this thin film. Traces of magnesium are proved to be blended into the Ca–P layer. Kinetics of formation of the Ca–P layer shows the high reactivity of this material in contact with a biological medium. However the Ca–P–Mg layer is finally dissolved after a few days of interaction. The absence of P in the initial glass matrix may explain that SiO 2 –CaO glass particles encounter great difficulties to achieve the transformation of their peripheral amorphous CaP layer into a more stable bone-like apatite phase.< Réduire