The objective of this study was to determine the effect of S. epidermidis 11047 on the pH and dissolution of 5 different bone substitute materials. Part 1 – Measured the pH, calcium and phosphate of the culture medium in the presence and absence of the 5 bone substitute materials before and after autoclaving. Part 2 – Measured the pH of the culture medium in the presence and absence of the 5 bone substitute materials before autoclaving and measurement of pH, calcium and phosphate 24 hrs later following incubation in the presence or absence of S. epidermidis. In part 1 it was concluded that autoclaving does not have a clinically significant effect on pH, calcium or phosphate levels of a culture medium in the presence or absence of the 5 bone substitute materials for the purposes of this study. There was a statistically significant reduction in pH, with a maximum decrease of 0.09. In part 2 it was concluded that there was a statistically and potentially clinically significant reduction in pH caused by the presence of S. epidermidis in all test samples and Cerasorb M (H4) is degraded in the presence of S. epidermidis.