A multiphase intervention trial based on education, implementation of criteria, and restriction, aimed at modifying the established clinical policy of mandatory preoperative screening for coagulation abnormalities, was carried out on five surgical wards of a general hospital. The education period did not influence the ordering of partial thromboplastin time tests, despite a significant posteducational change in surgeons' attitudes. In contrast, administrative restriction of coagulation test orders led to a 50% decline on four of the five study wards. We conclude that an educational intervention followed by administrative restriction may be considered an acceptable means of overcoming clinician reluctance to change well-established but redundant clinical policy.