Over the last decade much insight has been gained in the relationships between dosing regimens of antimicrobials and bacterial eradication and clinical efficacy. These pharmacokinetic-pharmacodynamic (PK/PD) relationships have become available as tools in individualising antimicrobial therapy. To be able to do this, the PK parameters of the antimicrobial in the individual patient have to be known or estimated, and the MIC of the micro-organism causing the infection, known. In our hospital, we have started a programme using this approach. Preliminary results suggest that dose optimisation leads to increased efficacy and lower costs.