Increasing resistance of micro-organisms to (multi-)antibiotics and the need for cost-control in the health service require a well-grounded antibiotic prescription policy world-wide. Many studies have shown that offering care providers information about desired behaviour does not automatically lead to desired behaviour in practice. Actually achieving changes in decision-making behaviour is determined by many factors. The present study aims to make an inventory of the factors that impede or facilitate appropriate use of antibiotics within departments of internal medicine at hospitals (two pilot hospitals). This information will then be used to formulate two intervention strategies to introduce existing guidelines at participating hospital departments, which will subsequently be tested for their applicability and effectiveness (two university hospitals, two large general hospitals and two medium size general hospitals). It concerns national guidelines developed by the SWAB (for bronchitis, pneumonia and sepsis). A before-after comparison will be made as well as a comparison between hospitals that got a 'basic' intervention (i.e. a hospital quality project) and hospitals with an additional personal-professional-orientated intervention. Indicators will be selected to determine whether the interventions were successful, including key parameters from the guidelines and data on quantity and quality of antibiotic prescription behaviour.