The primary objective of this study was to evaluate in vitro responses of MLO-A5 osteogenic cells to two modifications of the bioactive glass 13-93. The modified glasses, which were designed for use as cell support scaffolds and contained added boron to form the glasses 13-93 B1 and 13-93 B3, were made to accelerate formation of a bioactive hydroxyapatite surface layer and possibly enhance tissue growth. Quantitative MTT cytotoxicity tests revealed no inhibition of growth of MLO-A5 cells incubated with 13-93 glass extracts up to 10 mg/ml, moderate inhibition of growth with 13-93 B1 glass extracts, and noticeable inhibition of growth with 13-93 B3 glass extracts. A morphology- based biocompatibility test was also performed and yielded qualitative assessments of the relative biocompatibilities of glass extracts that agree with those obtained by the quantitative MTT test. However, as a proof of concept experiment, when MLO-A5 cells were seeded onto 13-93 B3 scaffolds in a dynamic in vitro environment, cell proliferation occurred as evidenced by qualitative and quantitative MTT labeling of scaffolds. Together these results demonstrate the in vitro toxicity of released borate ion in static experiments; however borate ion release can be mitigated in a dynamic environment similar to the human body where microvasculature is present. Here we argue that despite toxicity in static environments, boron-containing 13-93 compositions may warrant further study for use in tissue engineering applications.