The reaction of microspheres, made from three lithium borate glasses containing dysprosium oxide, with a phosphate buffered saline (PBS) solution (pH = 7.4) has been investigated over the temperature range from 22 to 42°C. All three glasses, two of which contained either 5 or 10 wt% alumina along with small amounts of magnesia and silica, reacted with PBS in the same general fashion but at rates dependent upon the glass composition. Rather than dissolving uniformly, each Dy containing glass reacted nonuniformly such that the Li, B, Al, Mg and Si in the glasses were selectively dissolved in the PBS while Dy reacted with the phosphate ions in the PBS to form an insoluble reaction product (gel) rich in Dy and P. The reaction started at the surface of the microspheres and proceeded inwardly until the entire microsphere had been transformed into a microsphere of different composition but of the same diameter. After being in the stifle joint of a rat for two weeks, the microspheres had the same general appearance as after reaction with PBS, suggesting that the microspheres had started to degrade and had reacted similarly in both PBS and the synovial fluid in a rat. These borate glasses are considered bioactive.