The activities in antibiotic drug-monitoring for improvement of antibiotic and/or antimycotic chemotherapies at the University Hospital Freiburg are represented. On the basis of examples such as cystic fibrosis, hand surgery and intensive medicine it is shown how antibiotic therapy can be improved by antiinfective drug monitoring. Furthermore knowledge can be gained, whether the concentration of the active compound is high enough and a rational therapy can be accomplished. This is increasingly interesting in particular in the context of the introduction of the DRGs. Improvements in patient-individual therapy can also reduce costs.