Gentamicin sulphate was mixed with two different sol-gel derived calcium silicates (akermanite or wollastonite). Each of the mixtures was isostatically pressed. Samples were immersed in simulated body fluid for 21 days. The presence of the antibiotic showed no effect on the in vitro bioactivity of the ceramics. For evaluating the gentamicin sulphate release, samples were immersed in a phosphate buffered saline solution for different periods of time. Most of the gentamicin sulphate was released during the first 7 days. However, akermanite showed a lower antibiotic release rate than that observed for wollastonite.