Laboratory services have a central role in surrounding the screening, diagnosis and management of patients and represent a significant expenditure for the NHS in Scotland, of which around 25% can be attributed to general practice use.  Some testing however can be regarded as ‘inappropriate’ which represents a substantial opportunity cost including the indirect costs of unnecessary further investigation of healthy individuals following false positive results.  This study aimed to evaluate the effectiveness and efficiency of two interventions to modify the test requesting behaviour of general practitioners in Grampian and Moray. A 2x2 factorial cluster randomised controlled trial design was used.  The two interventions, enhanced educational feedback and test report reminders, were introduced over a one year period.  The effect on the requesting behaviour of specific targeted tests was observed across the intervention groups.  The overall costs were considered taking into account the costs of delivering the interventions as well as potential savings. Target test requesting in the control group rose by 5.4% during the intervention period.  This compared to falls in test requesting in the feedback group (-2.2%), reminder group (-6.1%) and the group receiving both interventions (-16.8%).  Set-up and maintenance costs associated with the interventions compared very favourably with the potential savings that could be made due to reductions in test requesting. Both test report reminders and enhanced educational feedback are suitable vehicles for the delivery of educational interventions aimed at modifying laboratory test requesting behaviour.  Implementation of such into routine laboratory service could lead to substantial benefits for the NHS in Scotland due to a more rational approach to test use and an overall quality improvement in the diagnostic decision making process.