Change interventions in one form or another are viewed as important tools to reduce variation in medical services, reduce costs, and improve quality of care. With the current focus on efficient resource use, the successful design and implementation of change strategies are of utmost importance for health care managers. We present a case study in which macro and micro level change strategies were used to modify primary care physicians' practice patterns of prescribing diagnostic services in a safety-net's ambulatory clinics. The findings suggest that health care managers using evidence-based strategies can create a practice environment that reduces barriers and facilitates change. Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins.