Objectives: The aim of the study was to ascertain the efficacy of an intervention -where laboratory test costs were provided to clinicians as a pocket-sized brochure - to reduce the laboratory test costs over a 4 month period. Design: This was a non randomised intervention study where the intervention. group was compared to a similar and concurrent control group regarding the difference in laboratory test costs over a specified period in a specific year. The costs incurred were also computed for the same 2 groups over an identical time period and seasonal period in the preceding year, referred to as the control period. Setting and Subjects: The study was conducted in the Internal Medicine Wards at the Steve Biko Academic Hospital. The intervention period was during the winter months of May to August 2008 and the pre-intervention period was in the same months of the preceding year. Outcome measures: In the two (2007 and 2008) 4 month periods, for each patient admitted, the number of days in hospital and the laboratory tests ordered were computed. For the Intervention and control groups, pre and post intervention cost and days in hospital were estimated. The differences in logcosts per day were compared over time using ANOVA with group (1-2), time (1-2) and group*time as factors. Results: The mean cost per patient admitted in the intervention group decreased from R 2864.09 to R 2097.47 as a result of the intervention – a 27 % reduction in cost. The mean cost per day in the intervention group as a whole also decreased from R 442.90 to R 284.14 due to the intervention – a 36% reduction in cost. By contrast, in the control group, all costs increased in the control group from the pre-intervention to intervention periods – mean cost per admission in this group increased from R 1859.87 to R 2429.25 – an increase of 23%. The mean cost per day admitted in this group also increased from R 363.54 to R 371.92 – an increase of 2.2%. Conclusion: A heightened awareness of the cost of a laboratory test be it prospectively or retrospectively is a cost-effective and sustainable method of making doctors order tests rationally and appropriately.